When Mae West pronounced that too much of a good thing sometimes is a good thing, she probably didn't have the versatile molecule nitric oxide (NO) in mind. However, biologists at Washington University (St. Louis) have shown that a high concentration of NO in osteoclast bone cells might keep them from eating away too much bone, preventing bone loss associated with such diseases as osteoporosis. A team led by Philip Osdoby, a professor of biology, introduced an antibody into the osteoclasts that halted bone resorption, a process where bone is gnawed away by osteoclasts that are too numerous or too active. Biochemical tests showed that, after adding the antibody, an increase in NO occurred, followed by decreases in bone resorption. Osdoby believes that NO acts as a signal to turn the osteoclast off. "With a better understanding of how NO is regulated in osteoclasts, we may be able to develop new strategies to prevent bone loss," Osdoby adds. E-mail Susan_Killenberg@aismail.wustl.edu .