The effect of trans-4-amino-methyl-cyclohexane acid (AMCA) and a placebo preparation on the development of alveolitis sicca dolorosa (ASD) was investigated in a double-blind designed experiment. The preoperative registrations were age, sex, use of oral contraceptives, menstrual cycle, smoking, degree of impaction and operation time. The study included 120 healthy persons. Each person had bilateral impacted mandibular molars removed surgically at one session. AMCA (160 mg/extraction site) or placebor was applied in each socket after the operation. The postoperative course was evaluated on average 5 days later by the use of 13 different variables describing local and general discomfort. The incidence of ASD was 7.5% in the AMCA side and 5.0% in the placebo side. The result shows that a local inhibition of plasminogen activation by AMCA is insufficient to prevent the development of ASD. The occurrence of ASD and postoperative discomfort was not increased in women operated during the menstrual period. The usage of oral contraceptives is known to be associated with a high frequency of ASD. Women taking oral contraceptives may therefore postpone the operation to the withdrawal period of the pill, to reduce the risk of developing ASD. Postoperative pains and the consumption of analgetics were significantly increased in patients who were habitual smokers.