There are many methods for testing of the freshness of shellfish, but the organoleptic method has been put into operation in practice, because there are few other practicable methods.On freshness examination of oysters, we have developed a simple method, requiring about 1 hour for completion and measuring succinic dehydrogenase activity as the vital force in oyster gills using 2, 3, 5-triphenyltetrazolium chloride as indicator (TTC test). We have carried out practical control examination for 3469 samples of oysters and could get good results.1. In performing this test, the pieces of gill and 2ml of TTC solution are put into tube it is inverted twice, and held at 37°C for 40 minutes.TTC solution···1: 500 dilution; one portion of TTC in 500 portions of artificial marine water (or 3.4% NaCl), and it is adjusted to pH 6.52. Gills were the suitable parts of the oyster body for TTC test.3. Various normal shellfishes (200 samples, 10 species) have been tested and all of these have indicated positive results by TTC reaction.4. Oysters which have indicated negative results by TTC test, were in inadequate temperature or stored for a long time, or weakened by fresh water.5. Among the 3469 samples examined, 3348 were positive and others were negative by TTC test.