In order to compare the chemical composition of baboon and human amniotic fluid, 70 amniotic fluid samples were obtained from 58 normal baboon pregnancies at times ranging from 88 to 178 days (term, 180 days). Protein content averaged (+/- S.E.) 0.67 +/- 0.26 gm/dl, osmolality averaged 263 +/- 1.1 mOsm/kg, and pH averaged 7.74 +/- 0.034 units. These variables were not affected by length of gestation. Creatinine content increased parabolically with duration of gestation (r = 0.74; p less than 0.001). Forty percent of the samples had delta OD450 values of 0; the others had delta OD450 values ranging from 0.002 to 0.145. No decline in delta OD450 with gestational maturity was evident. These data suggest that the chemical environment of the baboon fetus is similar but not identical to that of the human fetus.