The purpose of these experiments is to determine the effects of foliar applications of benzylaminopurine (BAP) and gibberellic acid (GA) on tuber number production of seed potatoes. In field experiments conducted during 1989/90 cv. Mailen was used and BAP, 50 mg·l−1 was foliarly applied at (1) tuber initiation, 36 days after emergence (DAE); (2) 54 DAE; and, (3) 64 DAE. Under glasshouse conditions, in 1991/92 cv. Spunta was used and BAP 50 mg·l−1+GA 50 mg·l−1 were applied 30 and 37 days after planting/transplanting. In 1992 cv. Huinkul, Kennebec and Spunta were used and BAP 50 mg·l−1+GA 50 mg·l−1 and “Biozyme” (Techic SA), a commercial product with auxin (IAA, 32.2 mg·l−1), gibberellic acid (GA3, 32.2 mg·l−1) and cytokinins (zeatin, 83.2 mg·l−1) at 5 ml·l−1 were applied. In cv. Mailen, a higher tuber number in the seed fraction (<80 g) was found when BAP was applied at each of the three crop stages, while applications 54 and 62 DAE also increased tuber number in the 80–400 g fraction. As a result of BAP applications, tuber yield was also significantly increased. In the glasshouse experiments, cv. Spunta showed a significant increase in minituber production in 3 out of 4 cases, either if the mother plant came from in vitro generated plantlets or minitubers, or if GA + BAP or Biozyme was applied. It can be concluded that the use of these PGRs under both field and glasshouse conditions in cvs. Mailen and Spunta can result in increased tuber number in the seed fraction.Instituto de Fisiología Vegetal