To investigate the expression of nuclear transcription factor kappaB (NF-kappaB) in childhood acute lymphoblastic leukemia (ALL) and its significance, the biotin-streptavidin method and microscopy were used to detect NF-kappaB P65 protein in cells from 32 childhood ALL patients and 40 children without hematologic malignancies as control. The results showed that the positive expression rate of NF-kappaB P65 protein in cells from 32 childhood ALL patients was 87.50%, obviously higher than that in control group (12.50%) (chi(2) = 40.56, p < 0.01). In 28 childhood ALL patients with positive expression, the ratio of weakly positive (+) cases to all positive cases was 10.71% (3/28); the ratio of generally positive (++) case was 42.86% (12/28), and the ratio of strongly positive (+++) cases was 46.43% (13/28). While in the control group the of NF-kappaB P65 protein showed low expression with 100% (5/5). There was significant difference in the level of NF-kappaB P65 protein between ALL patients and control group. While the level of NF-kappaB P65 protein had no significent difference in morphology, immunophenotype (T-lineage ALL and B-lineage ALL) and the courses in the de novo and the relaspsed cases. It is concluded that NF-kappaB P65 protein expresses in cells of childhood ALL, the inhibition of NF-kappaB transduction pathway may have significant value in childhood ALL treatment. This study provides experimental basis concerning clinical treatment for ALL, when NF-kappaB is taken as a target.