We have investigated interstitial deletions of chromosome 8 in 70 colorectal carcinomas and 11 colonic adenomas using 11 microsatellite markers, including eight spanning the centromeric region of chromosome 8p (p11.2-p12). Allelic loss or imbalance was observed in 38 (54%) cancers and four (36%) adenomas. Twenty-eight (40%) of the cancers had deletions of 8p11.2-p12. Two distinct and independent regions of interstitial loss were found within this region. Fluorescent in situ hybridization, using an alpha satellite repeat probe to the centromere of 8p and two probes to the P1 region, was performed in four tumours that demonstrated allelic imbalance. Localized heterozygous deletions were confirmed in all four tumours. Eleven (16%) cancers had localized deletion in the region ANK-1 to D8S255 (P1) and a further eleven (16%) cancers had a less well localized deletion in the region defined by the markers D8S87 to D8S259 (P2). Loss of both centromeric loci was identified in a further six (9%) tumours. A functional significance for these two deletion regions was sought by correlation with primary and secondary tumour characteristics. Isolated P2 deletion was associated with 'early' T1 cancers (2p=0.0002), and were also identified in 3/11 adenomas. Conversely, interstitial deletions of the P1 locus were more frequently seen in 'locally invasive' T3/4 cancers (2p=0.015), and isolated P1 deletions were also associated with the presence of liver metastases (2p=0.016). Our data provide evidence of at least two genes within the 8p11.2-p12 region, mutations in which may confer different and independent roles in the pathogenesis of colorectal cancer.