The serum anti-malignin antibody (AMA) test determines the antibody to malignin, a 10,000-Da peptide present in patients with a wide variety of cancers. A total of 3315 double-blind tests demonstrated that AMA is a general transformation antibody, elevated in active nonterminal cancer, regardless of the site or tissue type, with sensitivity and specificity of 95% on the first determination and > 99% on repeat determinations. Data have not however been published yet that indicate whether, in daily clinical practice, the AMA test provides accurate prospective and predictive information. Forty-two physicians from 11 states, who ordered the AMA test, performed blind, report here on their results on 208 determinations in the first consecutive 181 patients and controls. Used in monitoring treatment in 56 patients, the test predicted or agreed 94.1% overall with the clinical status. Used in early detection in 125 patients and controls, of which 118 now have confirmed diagnoses, AMA was elevated in 21, all of whom were proven to have cancer; AMA was normal in 97, none of whom had cancer. Transient elevated AMA occurred in 3%, followed by normal values. Seven patients with still uncertain diagnosis who have had elevated AMA on repeated tests for 1 year or longer include six who are symptomatic, and three whose families have a high frequency of cancer. The conditions of these 7 may include undetected cancer because of the 118 with now certain diagnosis the AMA test predicted all correctly. From our experience, the AMA test should be used together with other routine procedures whenever signs and symptoms suggest cancer to facilitate early detection.