Five minor base ribonucleosides, primarily degradation products of transfer ribonucleic acid (tRNA), were evaluated as potential biological markers for patients with small cell carcinoma of the lung. The urinary concentration for pseudouridine, 1-methyladenosine, 1 -methylinosine, N2-methylguanosine, and N2,N2-dimethylguanosine was determined by means of reversed-phase high performance liquid chromatography and quantitatively expressed as a function of creatinine excretion. Comparisons were made with carcinoembryonic antigen (CEA) plasma levels. The total frequency of elevated values for the five nucleosides in pretreatment urine samples was directly related to stage of disease with 24/60 (40%) determinations increased in 12 patients with limited disease and 69/85 (81%) in 17 patients with extensive disease. For these same patients, CEA levels were elevated respectively in 2/11 (18%) of the former and 9/17 (53%) of the latter group. The frequency and degree of elevation of the nucleosidel creatinine ratios in pretreatment samples from patients with extensive disease was correlated directly with increasing number of metastatic sites. Of the five nucleosides, the mean number elevated was two for limited disease, 3-4 for extensive disease with one metastatic site, 4 for two or three, and 5 for four or more sites of metastases. Based on a summation of pretreatment nucleoside/creatinine ratios, a discriminant for survival was derived giving curves separating patients (P = 0.086) similar to the discriminant based on stage of disease. Although discordant results were noted, an overall correlation of 7511 agreement with clinical assessment was estimated in response categories when monitoring changes associated with therapy.