A study was conducted to evaluate the effects of varying drying temperature (Fresh, 85, 95 or 105°C) on the nutritive value of maize and response of broiler chickens to diets based on such grain, and supplemented with a microbial enzyme (Avizyme 1500). The chemical composition of the grain was affected by drying temperature. Starch and amylopectin contents were increased while there was a reduction in amylose content. These changes were expected to underlie the response of chicks to the diets. Total feed intake over 28 days was increased (P < 0.05) as a result of heat-treating the maize up to 95°C. The final body weight of chicks on the diet based on fresh maize was improved (P < 0.05) by the microbial enzyme supplement (MES). There was no effect of the enzyme supplement on body weight when assessed at earlier ages. Over the entire feeding period, feed conversion efficiency (FCE) declined (P < 0.001) with increasing oven temperature, regardless of the supplementation with the microbial enzyme. Body weight was influenced (P < 0.05) by the microbial enzyme only when assessed over the entire trial period. The weight of visceral organs, protein content and activities of pancreatic and jejunal digestive enzymes were unaffected by grain heat treatment or MES. The ileal digestibility of calcium was reduced (P < 0.001) on diets based on fresh maize and maize that was oven-dried at 105°C. Heat-treatment also improved (P < 0.05) the ileal digestibility of phosphorus in chicks on the diets without MES. There were no effects of grain heat treatment or MES on the ileal digestibility of energy, protein, Ca and amino acids. The results indicate some variations in grain quality as a result of heat treatment but the differences were not significant enough to stimulate major responses to the MES. Further studies should examine samples from commercial drying processes or samples obtained from a closer simulation of commercial conditions, to arrive at more practical conclusions.