The mental development of 37 infants with Down syndrome, allocated either to an experimental or control group, was assessed over a six-month period by an independent evaluator. The experimental group participated in biweekly therapy sessions designed to stimulate normal development while the control group received no intervention. The Griffiths Mental Developmental Scales were used to assess changes in the developmental status in the two groups, which were shown to be equal initially on a variety of variables. No statistically significant differences in mental development between the experimental and control groups were found. The early intervention regimen investigated in this study was not efficacious in altering the pattern of mental development in those Down syndrome infants participating in the program.