The mean activities (95% confidence interval; number of patients) for erythrocyte glucose-6-phosphate dehydrogenase (G6PD), hexokinase (HK), and pyruvate kinase (PK) in haemolysate of clinically normal neonates from Basrah, Iraq were found to be 3.29 (0.10; n = 456), 0.61 (0.02; n = 219), and 5.10 (0.07; n = 500), respectively, all expressed as U/10(10) RBC at 37 degrees C. Comparative values for apparently healthy adults were: 2.14 (0.06; n = 186), 0.41 (0.02; n = 46), and 3.61 (0.07; n = 243). Differences between sexes in the mean activities of each of the three enzymes were not significant (p > 0.5), being several times less than the corresponding 95% confidence intervals. However, differences were highly significant between neonates and adults (p < 0.001), presumably reflecting the greater proportion of 'young' cells and/or their programming for higher activity in cord blood. The neonate-adult difference (95% confidence interval) for each enzyme was: G6PD, 1.15 (0.43); HK, 0.20 (0.14); and PK, 1.49 (0.64). Some degree of G6PD-deficiency was observed in 7.9% of male and 9.7% of female neonates, whereas the frequency in adults was 9.2% and 11.8% for males and females, respectively. The higher frequency in females accords with expectations based on gene frequency estimations.