Placentas and fetuses from cases of induced midtrimester abortion and fetal loss (13 weeks of pregnancy or more) were examined microbiologically. In the series of midtrimester fetal loss, bacteria were isolated in 14 per cent and genital Mycoplasma in 37 per cent of the placentas. In induced abortion, 18 per cent of the placentas grew bacteria and in only one case out of 27 was a Mycoplasma strain isolated. Fetal organs yielded cultures positive for bacteria in 16 per cent and for genital Mycoplasma in 23 per cent of the spontaneous fetal loss material, whereas pyogenic cocci were isolated from fetal organs in 18 per cent and Mycoplasma in no case of induced abortion. In the positive cases, the fetal lungs were most often infected (in 34 out of 37 positive cases of spontaneous and 4 out of 5 positive cases of induced abortion). On the other hand, microorganisms could be isolated from the brain in only 5 out of 28 cases of spontaneous and none of induced abortion. In the series of fetal loss, positive microbiologic findings from the fetal organs seemed correlated to prolonged bleeding before abortion or labor and to premature rupture of membranes.