Heterosis observed in hybrids is the result of various physiological processes that occur at different stages of plant growth. A precise knowledge of the factors that contribute to heterotic vigor would help to manipulate heterosis expression in hybrids. We made a study to assess the physiological efficiency of rice hybrids during the crop growth period and to analyze the factors that contribute to heterosis expression. Six promising experimental rice hybrids were evaluated along with the popular check varieties Samba Mahsuri and Chaitanya during the 1995 wet season. Crop growth rate (CGR), leaf area index (LAI), and biomass production (BMP) were estimated at 15-d intervals from 15 to 60 d after planting (DAP). Harvest index (HI) and grain yield were recorded at harvest.