Post-treatment observation of two years' duration has confirmed preliminary data which indicated that a single injection of 2.5 million units of benzathine penicillin G, in early infectious syphilis, produces results equal, if not superior, to those obtained with schedules employing 4.8 million units of procaine penicillin and aluminium monostearate.Preliminary data suggest that a single injection of 2.4 or 2.5 million units of benzathine penicillin G may be inadequate for the treatment of asymptomatic neurosyphilis.Delayed reactions do not appear to be induced by the long-sustained blood-levels following the administration of benzathine penicillin G.Repeated injections of PAM increase the risk of reaction to treatment.