PURPOSE: The aim of the present study was to assess the clinicopatholgical significance of Bcl-2 oncoprotein expression in childhood non-Hodgkin's lymphoma (NHL). METHODS: We have assessed 16 cases of childhood NHL during last 6 years from 1990 to 1995. Bcl-2 oncoprotein expression has been semiquantitatively analyzed in paraffin sections from 16 cases of childhood NHL with 39 control cases of adult NHL. The expression of Bcl-2 oncoprotein was correlated with histologic grade, immunophenotype, proliferative activity as measured by immunostain of Ki-67 antigen, clinical stage, and survival rate (event free survival rate, EFS). RESULTS: 1) Bcl-2 oncoprotein expression significantly decreased according to increase of histological grade (P<0.05). 2) High Bcl-2 oncoprotein expression was more frequent in B-cell NHL than T-cell NHL (P<0.05). 3) Proliferative activity as measured by immunostain of Ki-67 antigen was negatively correlated with Bcl-2 oncoprotein expression (P<0.05). 4) Bcl-2 oncoprotein expression was not correlated with clinical stage (P>0.05). 5) EFS of patients was significantly correlated with Bcl-2 oncoprotein expression, that is, reduced EFS was demonstrated in the patients with low Bcl-2 oncoprotein expression (P<0.05). CONCLUSIONS: Thus Bcl-2 oncoprotein, as demonstrated immunohistochemically in routinely paraffin embedded tissue, can be restrictively used in prediction of prognosis and grade of childhood NHL, in aggrement with the role of Bcl-2 oncoprotein in blocking of apoptosis and indirect contribution to increase of cellular proliferative activity of NHL.