<p>Complementary meals were formulated from quality protein maize, soybean protein concentrate and cassava starch in the ratio 72:18.94:9.06 respectively. The flour blend was extruded to give three meals by varying three extrusion conditions (Temperature, moisture content and screw speed). The formulated diet had protein content values ranging from 20.09% in one of the extruded samples to 22.09% (dry weight basis) in the unextruded sample. The formulated meal (extruded and unextruded) and control diets were fed to rats for 28 days and the effects on body weight, organ weight, clinical signs, histopathology, haematology, and serum biochemical parameters were evaluated. There was no significant difference in the weight of the liver, kidney, pancreas, spleen, stomach and heart of the rats fed the three extruded samples and the casein diet at p ≤ 0.05. High protein Efficiency Ratio was recorded for the extruded meals (ranging from 2.24 to 2.45). There was significant difference at p ≤ 0.05 between the organ weights of the extruded meal and the unextruded meals. The rats fed the basal diet had the lowest (24%) Packed Cell Volume value while the values recorded for the extruded formulated meals were comparable to that recorded for the casein diet. Portal congestion and shrunken hepatocytes were however noticed in the liver of the rats fed the unextruded and basal diets. Extrusion</p><p>cooking had significant effects on the biological response of the rats to the formulated diet.</p>