To investigate the effect of normal fetal swallowing and amniotic fluid ingestion on small intestinal disaccharidase development, 13 pregnant New Zealand White rabbits underwent operation on day 24 of a normal 31-day gestation. The right ovarian fetus in the bicornuate uterus underwent esophageal ligation (EL), while the contralateral left fetus underwent cervical exploration only, and served as the control (C). Rabbits were sacrificed on gestational day 31, fetal somatic measurements obtained, and the midjejunum removed for determination of disaccharidase activity and protein content. There was one maternal death, and 9 of 12 fetal pairs survived the entire study period (75%). Results are reported as mean +/- SEM, analyzed by two-tailed Student's t testing with P < .05 being considered significant. Fetal weight was decreased in EL (48.6 +/- 2.7 g) versus C (51.4 +/- 3.2 g) (P = .06). Small intestinal length decreased in EL (49.2 +/- 2.0 cm) versus C (54.9 +/- 1.1 cm) (P = .01). Midjejunal protein content (mg/mL homogenate) was also significantly decreased in EL (38.4 +/- 3.4) versus C (46.2 +/- 3.7) (P = .05). Sucrase activity was not detectable in either group. Lactase activity in jejunal mucosa was not effected when expressed as units of enzyme per milliliter of homogenate (EL = 0.357 +/- 0.03 v C = 0.373 +/- 0.04; P = .70) and units enzyme per gram of protein (EL = 38.8 +/- 4.2 v C = 34.2 +/- 4.6; P = .44). We have confirmed previous studies demonstrating decreases in somatic growth, small intestinal length, and mucosal nutrient transport in rabbit fetuses following esophageal ligation.(ABSTRACT TRUNCATED AT 250 WORDS)