638 subjects from six tribes in Western Saudi Arabia were tested for haemoglobin and G-6-PD variants. In the bedouins of Harbi and Sahafi tribes there was no sickling but a low frequency of both G-6-PD deficiency (1.7%) and the Gd A+ variant (1.7%) in Harbi. In Mograbi and Mowallad tribes who immigrated recently from Africa, the frequency of Hb S was 4.1 and 3.5%, G-6-PD deficiency 7.5 and 8.5% and the Gd A+ variant 15.1 and 8.5% respectively, which are higher than in bedouins. In Ghamid tribe 4% had Hb S and there was a low frequency of both G-6-PD deficiency (4.8%) and Gd A+ variant (1.6%). However a new B slow variant is common among the Ghamid (16.1%). Hb S frequency in Zahran tribe was 2.6%. Six of the 12 g-6-PD deficient (screening) were found to be positive on starch gel electrophoresis.