DNA-based PCR with various sets of primers for TCR gamma/delta, and Ig heavy chain (IgH) genes were used to study clonality in childhood B-lineage acute lymphoblastic leukemia. Amplification of the IgH CDR-III was observed in 75 of 120 analyzed cases (62.5%). From all analyzed groups, the IgH gene rearrangement was most often observed in pre-B ALL (85.7%) and was rather rare in null-ALL (34.5%). TCR delta gene rearrangement was the most common, and was observed in 77 patients (64.2%). The typical pattern of rearrangements was defined as an incomplete V delta 2 to D delta 3, V delta 2 to D delta 2, or D delta 3 to D delta 2 recombination product. Rearrangements of TCR gamma gene we observed in 61 cases (50.8%). TCR gamma gene rearrangements were detected predominantly in null-ALL and early B-ALL (55.2% and 60%, respectively) and were rather rare in other groups. Of all eight V segments of V gamma I group, the most frequent gene usage concerns regions V gamma 2, V gamma 4, and psi V gamma 7. We have confirmed that IgH gene amplification, together with TCR gamma and delta gene amplification, provides a rapid, sensitive approach to assessing clonality in ALL almost in 100% of cases.