Transfer between a first and a second task, both available on the same piece of equipment, was studied as a function of degree of learning of the first task and of degree of similarity between tasks. It was found that acquisition of the second task was facilitated by practice on the first task, and that the facilitation increased directly with degree of first-task learning. Positive transfer also occurred with all degrees of inter-task similarity, and increased directly as similarity increased. Differential positive transfer resulting from variation of first-task learning lasted throughout all 60 acquisition trials on the second task; inter-task similarity produced differential positive transfer during only the first 30 trials. Some forgetting of the second task was present after a 24-hour rest; the forgetting neither varied as a function of the two main variables nor was attributable to their presence.