Exocoelomic fluid (N = 25) and amniotic fluid (AF) (N = 17) were retrieved by transvaginal puncture from 30 normal pregnancies being terminated for psychosocial reasons between 5-13 weeks of gestation. Biochemical analyses were performed on each sample including concentrations of urea, total protein, potassium, sodium, creatinine, hCG, and alpha-fetoprotein (AFP). The results were compared with values in maternal serum obtained at the same time. Significant correlations were found between gestational age and concentrations of urea (P less than .005), total protein (P less than .05), and hCG (P less than .001) in the exocoelomic fluid. Significantly (P less than .05) higher total protein levels were found in the exocoelomic fluid during the third month of pregnancy compared with the second month. Urea concentration and hCG levels were significantly (P less than .005 and P less than .001, respectively) lower in the exocoelomic fluid during the third than during the second month of gestation. Significantly higher protein (P less than .001 and P less than .001), potassium (P less than .005 and P less than .05), sodium (P less than .001 and P less than .05), and creatinine (P less than .01 and P less than .001) concentrations were found in the maternal serum compared with exocoelomic fluid and AF, respectively. The concentration of hCG was significantly (P less than .001) higher in exocoelomic fluid and significantly (P less than .001) lower in AF than in maternal serum. The AFP level was significantly (both P less than .001) lower in the maternal serum than in both fluids.(ABSTRACT TRUNCATED AT 250 WORDS)