The scientific interests of professor Andrzej K. Tarkowski have always revolved around experimental mammalian embryol- ogy. In 1959, he described the development of normal fertile mice from a single blastomere isolated from a 2-blastomere embryo; this was the first ever, successful experiment in the mouse reported in the literature. Later he proposed that during cleavage, the fate of blastomeres is labile and their further contribution to the inner cell mass or trophectoderm depends on their position in the morula (the so called "inside – outside hypothesis"). In 1961, Tarkowski reported the birth of chimaeric mice produced experimentally by the aggregation of two early embryos. This study again confirmed the great developmental flexibility of early mammalian embryos. He also devised a special technique for studying chromosomes in oocytes and early mammalian embryos, initiated studies on experimental parthenogenesis in the mouse, and studied developmental effects of induced chromosome aberrations such as triploidy, tetraploidy and diploid/tetraploid mosaicism. Tarkowski’s group also studied oocyte maturation, fertilization and nucleo-cyto- plasmic interactions in germ cells and early embryos, including remodelling of somatic nuclei transplanted to egg-cells. Some of the observations made in the latter studies have contributed to the development of techniques of mammalian cloning. Tarkowski was a head of the Department of Embryology from 1964 to 2003, and director of the Institute of Zoology at the Faculty of Biology in Warsaw University (1972-81 and 1987- 2003). In 2003 he retired, but nontheless continues his re- search. A very standard opening question: when did your interest in natural science begin, and why did you decide to study developmental biology, which at that time was called em- bryology? As I recall I undertook the decision to study biology about two years before completion of the secondary school. This decision was made under the influence of books and articles, Int. J. Dev. Biol. 52: 163-169 (2008) doi: 10.1387/ijdb.072377mm THE INTERNATIONAL JOURNAL OF DEVELOPMENTAL BIOLOGY www.intjdevbiol.com *Address correspondence to: Marek Maleszewski. Department of Embryology, Institute of Zoology, Faculty of Biology, Warsaw University, Warsaw, Poland. e-mail: maleszewski@biol.uw.edu.pl Published online: 14 February 2008 0214-6282/2008/$35.00 © UBC Press Printed in Spain and was reinforced by excellent lessons of biology taught by Dr Wanda Karpowicz. I was interested in laboratory biology rather than in natural science, I have never been a naturalist. The book that impressed me most was the academic textbook of Embryology by Emil Godlewski Jr (see article by Sliwa in this issue). This was the first volume (General Embryology), which dealt with reproduction, gametogenesis, cleavage and gastru- lation. I was fascinated by the earliest stages of embryogen- esis, by the variety of patterns of cleavage, and by movements of cells and cell layers during gastrulation. Right from the beginning, embryonic development fascinated me (and ap- pealed to me) because of its dynamism: each developing embryo is an exciting movie. The dynamic changes of one cell – the zygote – into progressively more complex embryo, larva and adult organism have always remained for me one of the greatest miracles of Nature. The second book, which chan- nelled my interest in embryology, was a thin book popularising experimental embryology: works of Driesch, Roux and of Hans Spemann and his colleagues on embryonic induction. In those days this kind of studies was called ‘mechanics of develop- ment’ and this was the title of the book. The author was Stanislaw Smreczynski, the student of Emil Godlewski,Jr., who himself was involved in this field of research before World War II, but after the war, as a head of Department of Zoology at the Jagiellonian University had directed the research of his team toward gametogenesis and early embrygenesis of insects (see article by Jaglarz in this issue). When I became a student of Biology my interest in embryol- ogy continued but it was purely theoretical because there were no animal embryologists at our Faculty who could help in ‘materializing’ my fascination. How did you, in mid 50’, come up with the idea to study the regulative potential of mammalian embryo? As far as I know at that time nobody at Warsaw University was study- ing this particular subject. Did you want to extrapolate experimental approach of Driesch, Horstadius and Spe- Early mammalian embryo: my love An interview with Andrzej K. Tarkowski MAREK MALESZEWSKI* and ANDRZEJ K. TARKOWSKI Department of Embryology, Institute of Zoology, Faculty of Biology, Warsaw University, Warsaw, Poland KEY WORDS: mammalian embryology, mouse, regulative development, isolated blastomere, chimaera