This study was aimed to investigate the clinical value of quantification of AML1/ETO fusion transcripts using real-time reverse transcription PCR. Fourteen AML1/ETO positive children out of 52 AML children were selected. A serial dilution of AML1/ETO plasmid was used as a template for the AML1/ETO real-time PCR. AML1/ETO was quantified according to the expression of the GAPDH housekeeping gene at new diagnosis and during/after chemotherapy and transplantation. SPSS statistics was used to analyze the data. The results showed that the ratio of AML1/ETO: GAPDH expression level at new diagnosis varied in the range 0.219-2.080 (median 0.648) among the patients, without relevance with percentage of blasts. The detection sensitivity was up to the dilution of 1:10(5). Six patients showed a slight decline of AML1/ETO (higher than 5 x 10(-2)) at 1 month, three of whom relapsed in the early stage and one later. Five patients had a higher level than 5 x 10(-3) at 3 months, three of whom relapsed. Four patients with always a higher level than 5 x 10(-3) all relapsed in early stage. After six months, four out of them with constant low-level expression (10(-4) - 10(-6)) were in continuous complete hematological remission (CCR). In another patient, a rapid rise of AML1/ETO transcripts could be detected at CR stage and he relapsed 5 months later. The AML1/ETO gene expression leveling off by 10(-5) - 10(-6) could be detected in 3 patients at their complete remission after 9 months. It is concluded that real-time RT-PCR is a suitable approach for quantifying AML1/ETO transcripts in monitoring of AML patients with t(8;21) during/after chemotherapy and provides data of diagnostic relevance.