Two experiments were carried out. The first study was designed to investigate the effects of percentage of reinforcement and the number of correct acquisition trials, when combined, on the number of responses to extinction and rate of lever-pulling of human subjects. The second study was designed to investigate the effects off percentage of reinforcement combined with number of reinforcements on the same dependent variables. Analysis of the data revealed: (1) resistance to extinction in both experiments, was inversely related to the percentage of reinforcement; (2) resistance to extinction was inversely related to the number of reinforcements but was not affected by the number of correct acquisition trials; (3) the mean rate of responding was inversely related to the number of reinforcements but was not affected by either percentage of reinforcement or number of correct acquisition trials; and (4) the number of responses per unit of time increased during acquisition and decreased during extinction in both studies. The results were discussed in relation to theories stemming from previous partial reinforcement studies. / Thesis / Master of Arts (MA)