The occurrence of mycobacteria was studied in organic horizons of coniferous forest soils in Finland and related to environmental variables, i.e. plate counts of other heterotrophic bacteria, microbial respiration rate, chemical soil characteristics, vegetational characteristics and climatic conditions in the study period. Mycobacteria were isolated from all samples (n=47), with plate counts varying from 4.5U10 4 to 1.2U10 6 cfu g 31 dry soil. The plate counts of mycobacteria correlated positively with those of other heterotrophic bacteria, microbial respiration rate and the contents of Ca and Mn. In factor analysis, the viable counts of mycobacteria and other heterotrophic bacteria, and respiration rate were grouped in the same factor emphasizing that mycobacteria and other heterotrophic bacteria had similar associations with environmental characteristics. The plate counts of mycobacteria and other heterotrophic bacteria and microbial respiration rate were similar in organic horizons of pine and spruce dominated forests. The large number of mycobacteria in all organic horizons indicates that boreal coniferous forest soils are important sources for these bacteria.