The decline in black fertility after the Civil War to its lowest level about the year 1936 does not fit the typical demographic transition pattern in which fertility declines postdate the initiation of mortality declines. Instead, for blacks much of the fertility decline (56 percent) was due to "involuntary infertility" related to venereal diseases. Circumstantial and historical evidence make a compelling case for venereal disease having a strong impact on black fertility, but a stronger link can be established between the two by using geographic techniques. Within the six-state region of the southeastern United States, the incidence of syphilis among black males, as discovered by the Selective Service in 1940-41, was related to the spatial pattern of black fertility by county in the same year, with the two variables correlating at fairly high levels. After World War II, black fertility rose dramatically due to the prevalence of antibiotic treatment for venereal disease. The pattern of fertility in 1960 showed substantial increases in virtually all counties in the six-state region and more particularly in those areas where fertility had been most depressed. After 1957, black fertility again began to decline. This time it was deliberate, owing to the increased adoption of family planning and the initiation of the final phase of blacks' true demographic transition. (CMG)