The toxicity of beryllium hydroxide (13327327) (Be(OH)2) and alloys was studied. Female rats were given one intratracheal injection of alloys. The animals were sacrificed from 1 to 18 months after treatment for autopsy and tumor assessment. Other rats were injected with 50 micrograms of Be(OH)2 or 2.5mg chrysotile asbestos (12001295); 10 months later, the Be(OH)2 group was given an additional 25 micrograms injection of Be(OH)2. These animals were sacrificed 6 months after the second injection, while the asbestos treated rats were sacrificed 20 months after treatment. Lungs were studied for histopathological changes. Lung neoplasms occurred in animals treated with beryllium metal, passive beryllium metal, and beryllium aluminum alloy. Most neoplasms were adenocarcinomas and adenomas. Animals treated with Be(OH)2 developed cuboidal and columnar cell metaplasia, bronchiolar alveolar cell tumors, squamous metaplasia, pulmonary adenomas, and adenocarcinomas. Older rats developed more tumors than younger rats. The asbestos treated rats developed fewer tumors than rats treated with Be(OH)2. The authors suggest that the beryllium metal and alloys that did not induce tumors might have been active at higher doses or longer treatment periods. Older rats may be more susceptible to tumor induction than younger ones.