Previous studies have demonstrated a rise in serum alpha-1-antitrypsin at advanced stages of malignancy. These, together with results of animal experiments with another anti-proteinase, aprotinin, have prompted studies of the plasma alpha-1-antitrypsin in the early stages of malignancy, using cervical carcinoma as a model. Measurements were made in three groups of individuals; negative cervical-smear women volunteers; hospitalised women with a positive result from the cervical-smear test; hospitalised women with a clinical cervical carcinoma. Elevated plasma alpha-1-antitrypsin levels were found in the “smear-positive” and “cancer” groups. Possible explanations for this increase are discussed and it is concluded that it occurs in direct response to the early stages of development of the tumor. Once a frank carcinoma has developed, maximal response has been attained, regardless of the degree of invasion or metastasis.