Within the past few years, the measurement of serum and tissue markers has had an increasing influence on clinical decisions about initial treatment and follow-up. Lung cancer illustrates the types and importance of these various markers. This review presents data concerning the most studied and interesting markers in non-small cell (NSCLC) and small cell lung cancer (SCLC). CEA, TPA, SCC-Ag, CYFRA 21-1, ferritin, CA19-9, CA50, CA242, H-K-N-ras mutations and p53 mutation seem to be the most prolific in NSCLC, while NSE, BN/GRP, CK-BB, NCAM, IL-2R, IGF-I, transferrin, ANP, mAb (cluster 5), Le-y and c-N-L-myc mutation are markers in SCLC patients. Some of these serum markers might be useful adjuncts for monitoring response to therapy, including early detection of tumour reactivation to allow curative therapy and rapid detection of treatment failure to allow change of the regimen. The study of these markers also may lead to a better understanding of the biological characteristics of lung cancer. The information derived from these biological studies represents the most promising avenue towards new treatment strategies, as well as attempts at secondary prevention.