The Penicillin Syphilis Group at the University of Pennsylvania has treated 746 patients with penicillin since Nov. 11, 1943. Of these, 283 had neurosyphilis. The average period of observation is 357 days, the longest period of observation being 719 days. One hundred and nineteen had been observed from 120 to 364 days, 55 for 365 to 599 days and 23 for 600 days and over. Thanks to the follow-up workers of the Institute for the Control of Syphilis, 97.7 per cent of these patients have been kept track of and returned for periodic observation and treatment. The material is classified by diagnosis and initial spinal fluid findings in table 1. The patients with negative spinal fluids at the outset showed symptoms against which response could be measured. POINTS DESERVING EMPHASIS IN THIS MATERIAL In order to be considered for penicillin treatment, the patient must have presented some