Rev.u.ta CotorrtJ.iano. de Mate.m.£ti.c.a.4 Vot. XXI V (1990), p6.gJ.. 153-171 ON SYSIDlS OF ORTH<XiONAL POLYNOMIALS WITH INNER AND END POI NT MSSES by Jairo A. CHARRIS and Guillermo RODRIGUEZ-BLANCO Abstract. A system of orthogonal polynomials related to the sieved ultraspherical polynomials is presented. It is shown that their orthogonality measure carri~s end point masses. It is also proved that the orthogonality measure of their first associated (numerator) polynomials has an embedded masspoint. Sumario. Se describe un sistema de polinomios ortogonales, relacionado con el de los ultraesfericos cribados, cuya medida de ortogonalidad tiene masas en los extremos del intervalo de ortogonalidad. Se demuestra tambien que la medida de ortogonali- dad de los polinomios numeradores correspondientes presenta una masa sumergida. 51. Introduction. We study in this paper two systems of or- thogonal polynomials defined by recurrence relations of the form * 1980 Mathe.matiC6 Subject C.taJ.J.~6~cation (1985 Revision) Prima- ry 33A65. Secondary 33A50-33A70. Key wo~ and PhAaJ.e.J.·. Orthogonal polynomials, recurrence rela- tions, continued fractions, orthogonality measures, mass points. The first author acknowledges partial support of the N.S.F. un- der grant Int. 8803099. 153