The absorption of oestrone (E1), oestrone glucuronide (E1G) and oestrone sulphate (E1S) from the small intestine of anaesthetized rats has been evaluated using the Doluisio in situ technique. Luminal disappearance of E1 was biphasic, which is consistent with a 3-compartment model; t1/2 alpha (first phase) was less than 5 min and t1/2 beta (second phase) approx 27 min for each concentration of steroid studied (trace identical to 10 nM, 1 microM and 10 microM). In contrast, luminal disappearance of E1G and E1S was monoexponential; t1/2 for E1G was 159, 229 and 299 min (trace identical to 200 nM, 10 microM and 100 microM respectively) and for E1S, 215, 174 and 192 min (trace identical to 10 nM, 10 microM and 100 microM respectively). There was a good correlation between the luminal disappearance data and recovery of steroid in bile. Adsorption of E1S was estimated from the initial rapid fall in luminal content within the first 5 min after drug administration. The study provides further evidence that E1S can be absorbed intact. Since saccharolactone only caused a reduction in E1G absorption of 32% we also conclude that part of the administered E1G was absorbed intact.