In patients with bronchogenic carcinoma of various types and stages, serum beta 2-microglobulin (beta 2-M) and carcinoembryonic antigen (CEA) were assayed simultaneously. The concentrations of serum beta 2-M and CEA were found to be statistically related to complete remission of the tumor (P less than 0.01). But it was also found that there was no correlation between the levels of beta 2-M and CEA (r = 0.0621). In follow-up, the CEA was found to be increasing incessantly as the disease progressed. For the level of serum beta 2-M, as the patients' condition got worse, it first rose, then dropped and became markedly lower before the patient died. The serum beta 2-M was often elevated 3-5 months earlier than CEA, and frequently resumed the normal level later than CEA after the carcinoma had a complete remission. With the progression of the bronchogenic carcinoma, elevation of beta 2-M was not necessarily a sign of poor prognosis. In contrast, with the serum beta 2-M markedly lowered after an initial elevation, the serum CEA became elevated, the prognosis was usually poor. The authors believe that, in patients with lung cancer, CEA produced from the lung cancer cells would give a level fluctuating with the size of the primary focus and the extent of the metastasis. But its positive rate is rather low. The serum beta 2-M is produced indirectly by certain immunologic function against bronchogenic carcinoma or its metabolites and not by the cancer cells directly. The positive rate of beta 2-M is high, so slightly is its false positive rate.(ABSTRACT TRUNCATED AT 250 WORDS)