The bcl-1 gene maps to chromosome 11q13 and has recently been shown to be a member of the cyclin gene family. Amplification of the chromosome region containing bcl-1 occurs frequently in breast cancer, squamous cell cancer, and other tumor types. We have hypothesized that amplification results in altered expression of the bcl-1 gene, contributing to carcinogenesis. In this work, we studied bcl-1 gene amplification and expression in a panel of human cell line. bcl-1 is expressed in all cell lines studied. The level of expression tends to be higher in amplified cell lines. We also screened these cell lines for int-2 and hst-1 expression, genes which are frequently coamplified with bcl-1. No int-2 expression was detected, and the two cell lines expressing hst-1 were unamplified. Our data provide support for the importance of bcl-1 in carcinogenesis.