Auxin (IAA, 5 × 10−5M) partially prevents the increase in the rate of phosphate uptake during ageing of potato tuber discs (Solatium tuberosum L. cv. Bintje), whereas fusicoccin (FC, 10−5 M) stimulates it. After the development of enhanced phosphate transport capacity, the response to fusicoccin is greater than with fresh discs. Complementary experiments on K+ (86Rb) absorption show that FC also slightly enhances the rate of K+ uptake, while IAA has no much effect. It is suggested that IAA acts specifically on the development of a mechanism which occurs during the ageing period, while FC action may be more directly linked to the system of phosphate transport itself.