Suckling (12- to 14-day-old) and weanling (30-day-old) rats were sacrificed 2 h after oral administration of 3H-labeled prostaglandin F2 alpha. Although radioactivity recovered from the stomach and small intestine (including contents) was slightly higher in sucklings (28.3 +/- 3.7%; n = 10) than in weanling rats (21.3 +/- 5.3%; n = 7), the liver of sucklings contained significantly higher amounts of counts (11.0 +/- 1.1 vs. 3.3 +/- 0.5%). Combined column and thin-layer chromatography of liver extracts showed more authentic prostaglandin F2 alpha in sucklings (11.0 +/- 0.5% of the liver counts) than in weanlings (7.0 +/- 1.1%). The liver of suckling rats contained a higher percentage of more polar metabolites (43.3 +/- 1.6 vs. 34.3 +/- 3.0%). These studies demonstrate differences in processing of oral prostaglandin F2 alpha in the early postnatal period.