Adenocarcinoma of the lung obtained at surgical resection was examined for mutation at codons 12, 13, and 61 of the oncogenes K-ras, H-ras, and N-ras, using polymerase chain reaction and oligonucleotide hybridization techniques. The mutation was detected in 18 of the 115 cases (15.7%), and 15 of 18 were at codon 12, 2 were at codon 13 of K-ras, and 1 was at codon 61 of N-ras. G to T transversions were most common. The ras gene mutations were more frequent in the male patients (P = 0.0048). No significant differences were found to be related to stage of the disease or tumor-nodes-metastases classification between positive and negative groups of the ras gene mutations. A history of tobacco use was not always a factor contributing to mutation. Of the completely resected group without lymph node metastasis, the 5-year survival rate in the ras-positive group was 53.3%, which was significantly poorer than the 83.6% survival rate in the ras-negative group (P less than 0.05). Our findings suggest that ras gene mutations may be prognostic, especially in the early stage adenocarcinoma of the lung.