The relationship between recent streptococcal infection and chorea gravidarum was studied in a young woman who had previously had Sydenham's rheumatic chorea. Unique circumstances made it possible to document the absence of streptococcal infection in the 15 months before the onset of chorea gravidarum. Thus it appears that chorea gravidarum represents the uncovering, through the agency of the special conditions of pregnancy, of previously latent rheumatic chorea. Recent streptococcal infection plays no role in its patho-genesis.