This study investigated the combined effects of early temperamental characteristics and environmental enrichment on a variety of developmental measures in nursery-reared rhesus monkey infants. Twenty-three infants, reared in either standard laboratory cages or enriched environments, were tested during the 1st month of life for interactive, motor, and temperamental capabilities and characteristics. At 8 months of age, all subjects were assessed on a second series of tests designed to measure their problem-solving skills, motor capabilities, and temperamental responses under challenge. Results indicated that enrichment was associated with higher scores on subsequent problem-solving and motor tests. However, such effects were found to combine with early temperament ratings. Specifically, individuals performing best on the 8-month tests had not only been reared in enriched environments, but also had been rated low on fearfulness during the early assessment. In addition, individuals scoring poorest had been rated as fearful initially in addition to being reared without enrichment. Results indicated that while high ratings on early laboratory assessments of fearfulness may be predictive of poorer problem-solving performance under challenging conditions, these adverse effects may be partially attenuated by environmental enrichment.