1. The effects of sodium octanoate and sodium salicylate on the rectal absorption of cefoxitin were investigated in healthy volunteers. Drug solutions were given either as a bolus or as a zero-order infusion. 2. On rectal infusion sodium octanoate and sodium salicylate both enhanced mean cefoxitin bioavailability (+/- s.d.) from 5.0 +/- 1.2% to 9.1 +/- 1.3% and 9.2 +/- 1.5%, respectively. After rectal bolus delivery octanoate increased the mean cefoxitin bioavailability from 7 +/- 3% to 17 +/- 3%, whereas bolus salicylate did not produce a statistically significant effect. All formulations were well tolerated by the volunteers. 3. It is concluded that both octanoate and salicylate are capable of enhancing rectal cefoxitin absorption in man; rate of delivery seems to be an important factor.