Galactose-1-phosphate uridyl transferase, the enzyme deficient in galactosemia, is demonstrated to be present in erythrocytes from fetuses of 12--30 weeks gestation. The specific activity and starch gel electrophoretic pattern of this enzyme in fetal erythrocytes is virtually identical to that found in erythrocytes postnatally. This enzyme was also studied in cultured fibroblasts from skin and amniotic cells and found to have similar specific activity and identical electrophoretic mobility in tissues from both sources. There does not appear to be a fetal isozyme for galactose-1-phosphate uridyl transferase in either erythrocytes or cultured fibroblasts. Thus, with fetal erythrocytes obtained by fetoscopy, it is likely that prenatal diagnosis of galactosemia can be rapidly and reliably accomplished.