Summary: Simultaneous inoculation of children and monkeys with measles virus of human origin produces in both, after a like incubation period, a syndrome which is similar except in point of severity. The syndrome in the children is that of typical measles; that in the monkeys is what we and others have regarded as typical of measles in this species. An examination of the results obtained in some 80 monkeys receiving in certain instances human and in others egg-derived measles virus, reveals no evidence of any difference in the picture produced by either of the materials. Both appear to be typical of measles in this species. Inoculation of 36 children with active egg-passage virus produced in 4 mild but definite measles, and in 7 others coryza with or without leucopenia and questionable Koplik spots appearing between the 8th and 15th days after inoculation.