The methodology for isolating rat peritoneal mast cell was established. The main pathogenic bacterial ultrasonicates of respiratory infection in GuangZhou area have been examined for their ability to release histamine from purified rat peritoneal mast cells. The results were as following: (1) 7 pathogenic bacteria can cause direct release of histamine from rat mast cells. The most effective histamine releasers were P. mira (histamine release percent is 26.89% +/- 6.70%), Strep. Pneu (24.16% +/- 3.71%), E. Coli (20.40% +/- 4.83%) and K. Pneu (17.91% +/- 4.60%). (2) Histamine release initiated by bacterial ultrasonicates was completed within 30 minutes E. Coli differed from K. Pneu induced histamine release was independent of its dose. (3) The products of K. Pneu did not induce histamine release directly and bacterial hemolysin may play a potent role in bacteria-induced release of histamine. Our findings provide some evidence for mechanism by which respiratory bacterial infection can precipitate or exacerbate attacks of bronchial asthma.