As a contribution to epidemiological studies on distribution of acute lymphoblastic leukaemia (ALL) subsets in different countries, we investigated blast cell immunophenotype in 54 children with ALL from the western part of Yugoslavia. The subtype incidences were: common, 75.9%; null, 7.4%; T, 11.1%; B, 1.9%; and unclassifiable, 3.7%. This resembles the ALL pattern registered in developed countries. Hence, differences in socioeconomic status between our population and developed European countries do not result in an appreciably altered incidence of childhood leukaemia subtypes.