The present study estimates the mean fat and solids-not-fat concentrations, and 305-day yields of fat, solids-not-fat, total solids and milk for three zebu breeds (Tharparkar, Sahiwal and Red Sindhi) and for halfbred F1 and F2 Brown Swiss ♂ × Sahiwal ♀ and ¾ Brown Swiss ♂ × Sahiwal 9 cattle maintained at this Institute during the period 1972–75. Mean fat and solids-not-fat concentrations ranged from 46·4 to 47·8 g/kg and 90·3 to 90·9 g/kg respectively, which were similar for all breeds. The 305-day fat, solids-not-fat, total solids and milk yields differed significantly between different breeds (P < 0–01). These yields were similar for the three zebu breeds (86 to 96 kg fat, 164 to 186 kg solids-not-fat, 250 to 282 kg total solids and 1 814 to 2 054 kg milk), but crossbreds showed significantly higher yields (125 to 171 kg, 242 to 332 kg, 368 to 503 kg and 2 670 to 3 676 kg, respectively), the highest being for F1 halfbreds. Season of calving had no significant effect on mean fat and solids-not-fat concentrations whereas the lactation yield parameters were found to be significantly higher for Tharparkar, Sahiwal and F1 Brown Swiss × Sahiwal cattle calving in the winter, followed in order by those calving in the monsoon and those calving in the summer. Selection of animals based on milk production alone was also found to increase the yield of milk constituents.