Porphobilinogen deaminase (PBGD), one of the enzymes in the pathway of heme synthesis, was found to be elevated in peripheral mononuclear cells of 60% of patients with epithelial tumors and metastatic spread, but only in 14% of patients with tumor and no evidence of metastases. The combination of both high lactic dehydrogenase and high PBGD afforded a sensitivity of 40%, but a specificity of 96% in diagnosing metastatic spread.