Toxicology, 46 (1987) 237--245 Elsevier Scientific Publishers Ireland Ltd. A STATISTICAL TEST FOR SYNERGISM OF TWO CELL GROWTH INHIBITORS PETER BLOOMFIELD* and BRIAN EASTWOOD Department of Statistics, North Carolina State University, Raleigh, NC 27695-8203 (U.S.A3 (Received February 16th, 1987) (Accepted May llth, 1987) SUMMARY Interaction of 2 inhibitors of cell growth can be detected by measuring the inhibiting effect of the 2 drugs separately and in combination. A control group is used as the basis for each comparison. We discuss a method for the statistical analysis of such measurements, when the basic observation is the number of cells harvested from a treated culture. Key words: Statistical test; Synergism; Antagonism; Growth inhibitor INTRODUCTION Noga et al. [1] explored the extent to which various drugs inhibited the growth of several cell lines, separately and in combination. The basic structure of each experiment was briefly as follows. A suspension of the cells in growth medium was prepared and equal amounts were measured into several wells. Each well was then treated with a specified drug regimen for a period of days, after which the cells were harvested and counted. The particular experiment with which we are concerned involved 4 such treatments, with 6 wells receiving each treatment. The 4 treatments were: C M -- T -- MT -- control, no drug administered; a specific dose of morpholine; pretreatment with a specific dose of theophylline; the combination of theophyUine pretreatment treatment. with morpholine *To whom all correspondence should be addressed. 0300-483X/87/$53.50 © 1987 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland 237