The site-dependent small-intestinal absorption pattern of griseofulvin was investigated in man. Griseofulvin was chosen as a model substance having extremely low water solubility and moderate lipid solubility. A conventional steady-state perfusion technique (triple-lumen tubing system with a 20 cm test segment) was applied. Dissolved griseofulvin (10.0 mg L-1) was perfused (10 mL min-1) during 160 min into different parts of the small intestine with the middle of the test segment between 85 cm and 270 cm beyond the teeth. Each of the ten healthy volunteers was examined twice with the test segment localized in different regions to allow for intraindividual comparisons. Mean drug absorption rates calculated from intestinal aspirate concentrations were similar in the two intestinal parts (proximal, 15.0 +/- 5.9 micrograms (20 cm min)-1; distal, 16.2 +/- 4.3 micrograms (20 cm min)-1; mean +/- SD). Absorption rate was strongly correlated to the amount of griseofulvin offered to the test segment per unit time. Extrapolating these findings it follows that an amount of griseofulvin, once dissolved, would be absorbed completely (> 99%) along 100 cm of the small intestine. A significant, positive correlation between the rate of transmucosal fluid transport and the absorption rate of griseofulvin was observed in the distal parts investigated.