A total of 1008 healthy unrelated young adult male police and military recruits, 317 from Brunei, 398 from Sabah and 293 from Sarawak, were examined for G-6-PD deficiency. The frequency in the 317 Brunei recruits, who were all of Malay origin, was 6.3 %. In Sabah the frequencies for the four main ethnic groups were 12.1 % in 165 Kadazans, 4.1% in 73 Malays, 3.4 % in 68 Bajaus and 24.2 % in 33 Muruts. In Sarawak the frequency was 11.6 % in 95 recruits of Malay origin. Three among 56 Ibans and one among 80 Sea Dayaks were found to be enzyme-deficient, but the numbers examined of these groups were too small for estimation of the frequency. The overall frequency for the Malay group in Brunei, Sabah and Sarawak was 7.0% in 485 persons examined.