Abstract The findings in 45 patients (42 males and 3 females) in Kuala Lumpur with acute haemolysis due to G-6-PD deficiency are reported. 36 were Chinese, 6 Malays, and 3 Indians, ranging in age from 3 days to 57 years. Drugs taken for the treatment of infections were usually the precipitating factors, and in the Chinese, Chinese medicine of unknown composition was important in bringing about haemolysis. In 2 Chinese it was precipitated by imported Chinese broad beans ( Vicia faba ); in one Malay child, a severe haemolysis with haemoglubinuria was precipitated by the ingestion of naphthalene moth balls. Haemolysis was acute and severe in most of the patients, and one died of uraemia. In Malaya, with a frequency of G-6-PD deficiency of about 2%, this deficiency poses an important problem in medical practice.