Studies on effect of seed species and their interacting influence on food utilization ofCallosobruchus maculatus clearly pointed out that rates and efficiencies of nitrogen utilization are determined by the composition of the seed also. Of the 3 species of seeds tested,Vigna unguiculata has significantly more nitrogen and water per unit weight than the other two seeds,Dolichos lab lab andPhaseolus radiatus. With increasing nitrogen content of the seed, rates of feeding, assimilation and metabolism decreased. On the other hand efficiencies of assimilation and net production increased. Nitrogen assimilation efficiency ofCallosobruchus maculatus ranged from 76·6% inDolichos lab lab to 85·8% inVigna unguiculata. The efficiency of accumulation of assimilated nitrogen was around 82%. The less nutritiousDolichos lab lab contributed more to the observed variance in the efficiencies of assimilation and production. The low efficiencies may be attributed to the presence of protease inhibitors.