Methacycline is more quickly absorbed and possibly more slowly cleared than tetracycline; it has a longer duration of action and it produces higher serum levels and higher antibacterial levels in vitro (Kunin, 1962;Remington and Finland, 1962;Te-Wen Chang and Weinstein, 1962;Limson and Guevara, 1963). To determine whether it might be more effective than tetracycline in the treatment of non-specific urethritis, the two drugs were compared in a double-blind clinical trial. Patients were asked not to take capsules within 2 hours of a meal (Kirby, Roberts, and Bardick, 1961) and to refrain from sexual activity and drinking alcohol while under surveillance. Follow-up attendances varied with the progress in each case. When persistence or recurrence of urethritis was recognized; cases were re-treated with the same double-blind procedure. At the conclusion of the trial the type of drug given to each patient at the initial or secondary treatmnent was revealed to the physician and the results were assessed on the basis of the recorded findings at 1 week, and 1, 2, and 3 months after starting treatment. The criteria for "cure" were the cessation of symptoms and the absence of urethral discharge coupled with a clear voided urine held for 5 hours (Harkness, 1950). No attention was paid to clear urethral secretion, early morning smears containing only occasional leucocytes, or to urine containing mucus. Cases of presumed relapse were not distinguished from those of presumed re-infection-both were classed as failure of treatment.