An intradermal test with formalin-inactivated egg-grown mumps virus was done on 109 household contacts of 42 cases of epidemic parotitis. Sixty of these individuals were skin-test positive and 49 negative. There were 12 contact cases of epidemic parotitis and 11 of them occurred among the nonreactors. There were 27 children who gave negative skin tests and they furnished 10 of the contact cases. The possible significance of this has been discussed. The various types of reactions encountered have been described and the frequent occurrence of relatively faint reactions in children noted. The validity of the test was supported by an obvious correlation with the incidence of secondary cases, past history and the fact that patients who were originally skin-test negative were positive several months later. It is concluded that the test is of value in determining susceptibility to epidemic parotitis. In view of the large number of clinically inapparent cases, the skin test should prove most useful in practice in removing unnecessary concern for infection by parents who do not recall having had the disease.