Research on the effects of smoking marijuana has tended toward two extremes--studies of chronic dispositional effects on people in long-term institutional settings or studies of acute effects on laboratory psychomotor tasks, physiological measures, and mood affect. The present studies represent a combination of these approaches. Human subjects will live in a comfortable, self-contained residential laboratory for 14-18 days. Their behavior will be observed and recorded, and access to all activities and to the other subjects will be programmed by the experimenters. The subjects will live in groups of three, engaging in ordinary activities available in the laboratory. Different experimental procedures from previous long-term motivational research will be used to study self-control, social interaction, and cooperation. Subjects will be required to devote time to low-valued activities to earn access to their most valued activities. Each subject's pattern of earning and using credit is a measure of self-control, and the pattern will be observed in both drug-present and drug-free conditions. The pattern will also be examined when subjects are required to earn access to other subjects, under both drug and no-drug conditions. Subjects will also be required to cooperate by working for each other, with and without self-administered marijuana smoking. In addition there are daily batteries of psychomotor and judgment tasks, as well as measurement of pulse rate and subjective states. The primary comparisons of performance for each procedure are between the drug and no-drug conditions. If marijuana results in a weakening of the effects of motivational variables, subjects will show less accumulation of resources and more erratic control of access to valued activities and access to other subjects.