The time course for the development of acuity was followed in two experimentally esotropic infant monkeys (Macaca nemestrina). Surgical esotropia was produced at 6 days postnatal. Acuity values for both eyes of both infant monkeys were found to be normal through 4 weeks postoperative. After this period of delay, amblyopia began to emerge. The deviated eyes showed poorer acuity than the nondeviated eyes at every subsequent age tested. These data support a developmental hypothesis for the emergence of strabismic amblyopia.