A randomized, double-blind, placebo-controlled, multicenter study was conducted to ascertain the contribution of Fiorinal and codeine phosphate to the efficacy of Fiorinal with Codeine in relieving the pain, tension, and muscle stiffness associated with tension headache. Patients were given Fiorinal with Codeine, Fiorinal alone, codeine alone, or placebo for use during two separate headache attacks at least 24 hours apart and were asked to rate the effectiveness of the assigned medication on each occasion. The various symptoms of tension headache were evaluated by the patient 0.5, 1, 2, 3, and 4 hours after ingestion of the study medication. At the final patient visit, the investigator assessed the effect of treatment on the three chief components of tension headache, head pain, psychic tension, and muscle contraction. Fiorinal with Codeine was generally significantly more effective than placebo or Fiorinal alone in improving all patient-evaluated items between the second and the fourth hours after administration. The combination was also generally significantly better than codeine alone with respect to pain severity, pain relief, the ability to perform daily activities, and average pathology. The three variables rated by the physician also were generally reduced significantly more with the combination than with placebo or Fiorinal alone. Side effects occurred in only one patient treated with Fiorinal with Codeine.