The phenotypic and quantitative relationship of red cell acid phosphatase with haemoglobin, haptoglobin, and G6PD phenotypes was investigated in three populations in the Sudan and one population in Nilgiris, India. No significant consistent association of red cell acid phosphatase phenotypes was observed with these polymorphisms. However, there was a lack of acid phosphatase AB in G6PD deficient subjects from Nilgiris. The relative quantitative expression of red cell acid phosphatase genes PA, PB, and PC was 1.0, 1.2, and 1.3, respectively. The red cell acid phosphatase activity was higher (15%) in the presence of raised haemoglobin A2 and in sickle cell anaemia (21%). Those with Hp2 had 18% higher level of acid phosphatase than those with Hp1. G6PD deficient subjects had a lower level of acid phosphatase activity (20%) than those with normal G6PD activity.