Abstract The characteristics of renal transport of a homologous series of hydrocarbon derivatives of sulfamyl benzoic acid were examined in cortical slices of rabbit kidney. The length of the hydrocarbon substituent varied from C 1 to C 5 and the compounds differed from the previously examined probenecid series  in having only one hydrocarbon substituent, instead of two, at the sulfamyl group. Transport rate, maximal accumulation and affinity of the monosubstituted compounds for transport were enhanced by an increase in the length of the hydrocarbon substituent. In comparison with the probenecid series less binding by tissue constituents under anaerobic conditions was observed. Competition experiments indicated that the monosubstituted compounds were transported by the same transport system as that of PAH. Octanoate and fumarate exerted a biphasic effect on accumulation (i.e. stimulation at low and inhibition at high metabolite concentrations), as in the case of other organic anions. In comparison with probenecid the monosubstituted compounds were more susceptible to inhibition by PAH, fumarate and octanoate. Nevertheless, pentylsulfamyl benzoic acid exerted a somewhat more powerful inhibitory effect on the accumulation of phenol red and PAH than did probenecid. The monosubstituted compounds were less hydrophobic than probenecid as evidenced by less extractability from an aqueous phase into an organic liquid (1,2-dichloroethane). It is concluded that for the sulfamyl benzoic acid derivatives moderate hydrophobicity results not only in a higher affinity, but also in an enhanced turnover rate of the carrier system for organic anions.