The prognostic value of some pretreatment blood tests was analysed in a follow-up study of 189 patients with non-small cell lung cancer diagnosed in West-Norway between 1976 and 1985. At diagnosis 100 patients had stage III/IV disease. Five-year survival calculated with the life-table method was 12%. In univariate survival analyses significant prognostic factors were stage III/IV disease, weight loss, elevated lactate dehydrogenase, gamma glutamyl transferase, erythrocyte sedimentation rate and alkaline phosphatase, thrombocytosis, leukocytosis and anaemia. In multivariate survival analyses with the Cox's regression model stage III/IV disease, elevated lactate dehydrogenase, thrombocytes and erythrocyte sedimentation rate were significant prognostic factors. It is concluded that these blood analyses at diagnosis in non-small cell lung cancer patients may give additional prognostic information. The need for multivariate analyses is also demonstrated.