Of 36 persons ill with trichiniasis (i.e., two to six weeks after infection) 25 (70 per cent) gave positive immediate skin reactions following intradermal injection with 0.1 cc. of a 1:10,000 dilution (in terms of dry weight of powder) of a saline extract of Trichinella spiralis larvae. An additional 8 reacted to a 1:500 dilution of the antigen making a total of 33, or 92 per cent positive. Of 39 persons tested from three to twenty-two months after infection, 19 (49 per cent) reacted to the 1:10,000 dilution and an additional 12 were positive to a 1:500 dilution, a total of 31 or 80 per cent positive. Of 13 persons ill three and one-half to seven and one-half years prior to the test, 3 (23 per cent) were positive to the 1:10,000 dilution, and 5 more reacted to the 1:500 dilution, a total of 8 or 62 per cent positive. One hundred and four control persons from Rochester, New York, showed an incidence of 9 per cent positive with the 1:10,000 dilution and a total of 18 per cent positive with both the 1:10,000 and 1:500 dilutions. Forty-seven control persons from San Francisco, California, showed an incidence of only 4 per cent positive to the 1:10,000 antigen and 6.5 per cent positive with both the 1:10,000 and 1:500 dilutions. Ninety-two persons from southern Louisiana infected with Trichuris trichiura showed an incidence of 18 per cent positive with the 1:10,000 dilution and a total of 62 per cent with both the 1:10,000 and 1:500 dilutions. The practical use of the skin test in the diagnosis of trichiniasis is discussed.