The levels of 23 protein components of the sera of 84 patients with uterine cervical cancer undergoing radiotherapy were determined by a single radial immunodiffusion method, before radiation therapy, after whole pelvic irradiation, and after intracavitary irradiation using a remote after roading system (RALS). We examined the correlations between changes in serum protein fractions and the prognosis of the patients. The patients with uterine cervical cancer were treated with combined external irradiation of 60Co gamma-rays or 10 MV X-rays, and RALS therapy. The levels of the same protein components were also measured in 21 normal adult women as a control. All patients were observed between 4 years and 8 years after radiation therapy. In the pretreatment sera obtained from patients with uterine cervical cancer, the concentrations of prealbumin (Prealb), alpha 2HS glycoprotein (alpha 2 HS), alpha 2-plasmin inhibitor (alpha 2PI), transferrin (Tf), plasminogen (Pmg), albumin (Alb), IgM and hemopexin (Hx) were significantly lower than those normal controls. However the serum concentrations of: alpha 1-antichymotrypsin (alpha 1 X), haptoglobin (Hp), C9, fibrinogen (Fib), ceruloplasmin (Cp), alpha 1-acid glycoprotein (alpha 1AG), alpha 1-antitrypsin (alpha 1AT) and C4 were elevated. At the completion of whole pelvic irradiation and RALS therapy, the Hp, C4, and Fib levels were significantly lower than those before radiation therapy, whereas Prealb, alpha 2HS and alpha 2PI were elevated. In patients who had lived between 4 years and 8 years after radiation therapy, the Cp, alpha 1 AG, Hp and C9 levels measured before radiation therapy were reduced significantly, while Tf was elevated compared with patients who died within 4 years. In those who had lived more than 4 years, the alpha 1 AT, Hp, alpha 1X, Cp and C9 levels measured after whole pelvic irradiation were reduced significantly; while the C4 level was elevated. In cases of uterine cervical cancer followed for a period of 4 to 8 years after radiation therapy, multiple regression analysis was used to determine whether increased concentrations of serum protein fractions were associated with good prognosis for the original disease. Tf, Pmg, and alpha 1AT before radiation therapy were positively correlated with survival, whereas AT III, Cp, C1Inh, IgA, alpha 1 AG and C9 showed negative correlations. After whole pelvic irradiation,Pmg, C4 Prealb, Alb,alpha 2M and Hp were found to be positively associated with survival, whereas Tf, alpha 2PI, AT III, alpha 1 AT,C1Inh, C9 and IgA were negative factors.