postpartum. However, beginning at day 10 and for each subsequent time period assayed thereafter, there was a statistically significant reduction in the number of splenic PFC observed in the smokeexposed animals. On day 10, the PFC response of smoke-exposed mice was reduced by 3375, on day 14, there was a 60% reduction, whereas animals exposed to smoke from 4-10 wk showed a 90?& reduction of the splenic PFC response. Speculation fare (25), indicated that Lo definitive conclusions could be drawn at that time. Rickzeh et al. (17) found that exposure of female rats to high doses of cigarette smoke during gestation did not result in significant differences in regard to litter weight, litter size, number of implantation sites, the incidence of resorptions, or in the appearance of skeletal abnormalities when compared to untreated controls, thereby supporting the previously mentioned report. Interestingly, in a study of sera obtained at delivery from a large number of pregnant women, Nymand (15) found a significantly lower incidence of lymphocytotoxic antibodies in women who smoked compared to a matched control group of nonsmokers. In addition, the smokers had a higher incidence of urinary tract infections as well as febrile and nonfebrile virus diseases during pregnancy than did nonsmokers. Unfortunately, no mention was made of the physiologic or immunologic status of the offspring in the above study nor is any information available regarding the effect of cigarette smoke on the maturation of the immune response. The finding that exposure of newborn mice to cigarette smokeThe purpose of the present study was to determine effect, resulted in a marked inhibition of the maturation of the splenic if any, smoke exposure of neonatal animals would have on the antibody response to SRBC is consistent with previous reports of maturation of immune responsiveness as measured by the appearthe immunosuppressive effects of cigarette smoke exposure in ex~erimental animals and humans. I t is wssible that this inhibitorv ance of splenic PFC's. effect is manifest at the level of the macrophage or the thymusderived lymphocyte, both of which have been suggested to be functionally immature in the newborn mouse.The immune response to many, if not most, immunogens appears to involve a complex series of interactions among three heterogeneous functional cell types: bone marrow-derived lymphocytes (B cells), thymus-derived lymphocytes (T cells), and macrophages. It is now well accepted that the ability to respond immunologically to challenge with foreign materials undergoes a process of maturation that begins during embryonic development (21). Whereas it has been suggested that most cases of immunologic immaturity in neonatal animals or immunologic deficiency in adults can be attributed to the absence or a functional abnormality in immunocompetent B and/or T lymphocytes, there is also evidence to suggest that immaturity or defects in macrophage function can account for a lack of immune responsiveness (1, 7).Exposure of experimental animals and h...