Exposure of fifteen children to mumps virus of fifth amniotic passage in chick embryos led to involvement of the salivary glands in six, orchitis in the absence of other manifestations of mumps in one, and to no signs of illness in eight. Attempts to isolate virus from the saliva of these individuals gave the following results: 1. All patients with involvement of the salivary glands excreted virus beginning on the 11th to 15th day after exposure, 2 to 6 days prior to onset of clinical signs of disease and extending up to the 4th day of illness. 2. The patient with primary orchitis without any recognized involvement of the salivary glands excreted virus for 2 days, beginning on the 15th day after exposure and 10 days prior to his illness. 3. Six of the eight children classified as having inapparent infections because of their serologic response in the absence of clinical signs of illness, began to excrete virus on the 15th to 16th day after exposure for from 1 to 9 or more days. The epidemiologic significance of these data is discussed.