In 1975, a survey was carried out in Canada to determine the primary and acquired drug resistance of M. tuberculosis isolates to isoniazid (INH), para-aminosalicylic acid (PAS) and streptomycin. The results of this investigation were compared with those of the primary drug resistant study of Armstrong, undertaken in 1963-64. It revealed that primary drug resistance has increased from 4.9% to 6.3%. The increase is mainly due to immigrants having arrived in this country during the last 12 years. In these newcomers the primary resistance rate was 11.5%. Moreover, 57.8% of the immigrants examined in the survey were of Asian origin, with a drug resistance rate of 11.7%, while 15.6% had arrived from South Europe with a resistant ratio of 16.7%. In retreatment cases, the national average of drug resistance was 26.4%. Among the Canadian provinces, the highest drug resistance rate in retreatment patients (40%) was found in Quebec. While in primary resistance Streptomycin exhibited the highest incidence, in retreatment cases isoniazid resistance proved to be more frequent. In natives, the rates and patterns of primary and acquired resistance were very similar to those observed in other Canadian born patients.