In Porto Velho, where there was a sufficient number of malaria cases among normal males to assess the variance from the whole male normal population, a slight decrease was observed in the adjusted male median among malaria positive normal males (8.7 U/g Hb 95% CI 8.0–9.7) compared to all normal males, with a P value of 0.004 but with significantly overlapping confidence intervals. The gene discussed is GSTM1; the disease is malaria.