The possible effects of maternal spermicide use on birth characteristics of offspring were examined in two studies. First, birth weight of offspring was examined in a cohort study of 302 women who reported using spermicides and 716 women who used no contraceptive methods in the year prior to pregnancy resulting in a 1974 live birth (without a malformation) in Upstate New York. There was no evidence that spermicide use prior to the last menstrual period (LMP) had an effect on mean birth weight or on the proportion of lower weights. Mean birth weight of female births was significantly lower in post-LMP spermicide users than in pre-LMP-only spermicide users and no-contraceptive users. In multiple linear regression analyses of birth weight among births to spermicide users, including maternal smoking during pregnancy and other variables, time of discontinuation of spermicide use was an important predictor of female (but not male) birth weight. In the second (case-control) study of 715 Upstate New York births with selected birth defects and 715 control births (matched on maternal age and race), no significantly increased relative risks were associated with maternal spermicide use prior to LMP or after LMP. Based on small numbers, relative risks for post-LMP spermicide use were greater than 1.00 for hypospadias (8/2 or 4.00, not significant) and for limb reduction defects (6/3 or 2.00, not significant).