We have examined alterations in six oncogenes--H-ras, K-ras, N-ras, myc, fos, and N-myc--in nine primary human colon tumors. Tumors were obtained within an hour of resection; as a control for each tumor, adjacent normal colon tissue was also obtained. Deoxyribonucleic acid extracted from each tissue sample was assayed by digesting with appropriate restriction endonucleases and, after gel electrophoresis and transfer to nitrocellulose, hybridizing with radiolabeled oncogene probes. Amplification of the myc locus, relative to adjacent normal colon tissue, was observed in two of these tumors; by dot-blotting, it was estimated that myc was amplified twofold to fivefold in each tumor. No rearrangements of myc, however, were observed in any of these tumors. Examination of the H-ras alleles of these nine tumors revealed that eight possess only "common" alleles of this gene, and that each was identical to its control. Normal colon DNA of the ninth patient, however, was found to possess both a "common" and a "rare" allele, and the "common" allele of H-ras appeared to be deleted in the tumor DNA of this patient. A restriction polymorphism indicative of a mutation in the 12th codon of K-ras was not found in any of these tumors, and we observed no evidence of rearrangement of amplification of the N-ras, K-ras, fos, or N-myc genes.