A rapid flocculation test for the diagnosis of trichinosis is described. The antigen was prepd. by sensitizing colloidal particles of bentonite with a saline extract of the larvae of Trichinella spiralis and it remained stable for a period of months. The technic of antigen prepn. is described. The test was performed by adding one drop of the sensitized bentonite particles of 0.1 ml. of 2-fold serial dilutions of human sera on a wax-ringed slide. The slide was rotated for 15 min., after which the reactions were read. Comparison of the flocculation testwith the complement-fixation test indicated that they were equally sensitive and apparently gave no false positive reactions. The flocculation test described can be performed in a few minutes and does not require highly trained personnel. Preliminary studies indicate that the test may be applied to the diagnosis of brucellosis, tularemia, and certain parasitic diseases besides trichinosis.