One hundred and seven amniotic fluid samples from 70 patients, between 14 and 44 wk gestation, were studied for lysozyme enzyme content using a modification of the method of Parry, Chandon, and Shalani. A progressive increase in the absolute concentration from levels of 5.1 to 18.8 μg per milliliter at 38 to 40 wk was found. A similar increase is apparent when the results are correlated with the amniotic fluid total protein. These data were expressed as milligrams of lysozyme per gram of total protein. This increase in lysozyme occurs despite a decrease in the total protein content and an increase in volume. The lysozyme levels fall after 40 wk gestation. The possible function of lysozyme in the amniotic fluids is discussed.