Seasonal photosynthetic patterns of Loring peach (Prunus persica (L). Batsch) leaves were monitored throughout the 1974 growing season. Using leaves on detached branches, CO2 exchange was measured under controlled light and temperature conditions. Net photosynthesis rate varied from 9 to 12.4 mg CO2 dm(-2) leaf area h(-1) and was correlated with fruit development, with the highest values occurring during the final stage of fruit maturation. The proximity of fruits to leaves also regulated photosynthesis, with the highest rates occurring in leaves closest to fruit. Soluble-sugar content in fruits and fruit yield were highest in tree areas with greatest exposure to direct sunlight although leaf area was evenly distributed throughout the tree. Light and temperature optimum for photosynthesis in peach leaves was 9.5×10(-3) erg cm(-2) s(-1) and 30°, respectively.