This study was initiated to evaluate the effect of N and P fertilization on yield and yellow berry development in bread and durum wheat. Two wheat varieties, Cocorit 71 (durum) and Cajeme 71 (bread wheat), were grown under irrigation at The University of Arizona Experimental Farm, Marana, on Pima clay loam soil during the 1976-77 growing season. Twelve treatments involving four levels of N and three of P were arranged in a randomized block design with six replications. These were 0, 168, 252 and 336 kg N/ha and 0, 44.8 and 89.6 kg P/ha. Prior to harvest, samples were taken and analyzed for number of heads, head weight, straw weight, and grain weight. Grain yield was determined at harvest. Percent yellow berry content, number of grains per head and number of grains per 25 g were determined later. Yellow berry and vitreous grains were analyzed for N content. Grain yield increased with increased N and P but N in excess of 252 kg/ha decreased yields of both varieties slightly. The maximum grain yields of both varieties were associated with 89.6 kg P/ha. Yield increases were primarily due to production of more heads and grains as well as increase in grain weight per unit area. Percent yellow berry decreased with increased N with no significant effect of P. Percent N in yellow berry grains was generally lower than in vitreous grains