The influence of dietary omega-3 fatty acid supply on visual acuity development was evaluated in very low birth weight (VLBW) infants using visual-evoked potential (VEP) and forced-choice preferential-looking (FPL) procedures at 36 and 57 wk postconception. The VLBW infants born at 27-33 wk postconception were randomized to one of three diet groups: corn oil, which provided solely linoleic acid; soy oil, which provided linoleic and alpha-linolenic acids; or soy/marine oil; which was similar to the soy oil formula but also provided preformed long chain omega-3 fatty acids. The VLBW infants in the soy/marine oil group had higher omega-3 levels in erythrocyte membranes and better VEP and FPL acuities at 36 and 57 wk than infants in the corn oil group. The soy oil group had intermediate omega-3 levels in erythrocyte membranes and significantly poorer VEP acuity at 57 wk compared with the soy/marine oil group. Only the soy/marine oil group had acuities comparable to the "gold standards" of VLBW infants fed human milk and preterm infants who were born and tested at 35-36 wk postconception. In addition, VEP and FPL acuity were poorer in a nonrandomized group of formula-fed full-term infants than in breast-fed full-term infants. The results suggest that dietary omega-3 fatty acid supply may play an important role in early human visual development.