The prognostic importance of pretreatment delayed hypersensitivity skin test reactivity was determined in 154 newly diagnosed, carefully staged and agressively treated small cell lung cancer patients. One hundred twenty‐one patients were reactive to at least 1 of 5 skin test antigens and 33 were anergic. Skin test reactive patients survived significantly longer than anergic patients. This result was expected since there was a significant trend for reactive patients to have good performance status (P = 0.005) and low tumor burden (P = 0.005) compared to anergic patients. The principal finding of this study was that skin test reactivity was of prognostic utility primarily in otherwise good prognosis patients, i,e., individuals with good performance status and low tumor burden. In this group anergy was associated with significantly shortened survival (P = 0.025). In poor prognosis (poor performance status and high tumor burden) or intermediate prognosis (either poor performance status or high tumor burden) patients skin test reactivity or anergy had no significant influence on survival.