We investigated the expression and deletion of DLC-1 (frequently deleted in liver cancer gene), first reported in 1998 and having a high homology with rat p122RhoGAP in hepatocellular carcinoma (HCC). Six (20%) of 30 human HCC samples and 2 (40%) of 5 HCC cell lines were found to have no detectable DLC-1 expression by reverse transcription-PCR. Homozygous DLC-1 deletion was detected by Southern blotting in two of six HCC samples and in both HCC cell lines with no DLC-1 expression. Transfection of DLC-1 into 5 HCC cell lines (two with DLC-1 deletion and three with intact DLC-1) showed significant growth inhibition in these two HCC cell lines with deleted DLC-1 with both 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and colony formation assays but not in three other HCC cell lines with intact DLC-1. Our findings suggest that DLC-1 may play an important role in hepatocarcinogenesis.