A total fraction of triterpenic glycosides from Cucumaria japonica named cucumarioside was used as a stimulator of nonspecific resistance to bacterial infections in mice. After intraperitoneal administration to mice subsequently infected with various strains of E. coli and Proteus mirabilis, cucumarioside provided survival of 40 to 90 per cent of the infected animals against 100 per cent in the control group. The protective effect directly depended on the dose of cucumarioside. It was optimal to administer the preparation 3 days before the infection. When the preparation was administered at such periods LD50 for Neisseria meningitidis BT-2 and Salmonella minnesota SF 1111 lowered 5 and 4.3 times, respectively. Therefore, the total fraction of triterpenic glycosides from Far Eastern holothuria had a marked ability to increase natural resistance of the animals to infections caused by various gram-negative organisms.