The usefulness and safety of the fine-needle aspiration biopsy (FNAB) technique for the study of liver cell changes were evaluated in rats. Repeated punctures of the same liver lobe (40 punctures in 10 weeks) caused small necroses and hemorrhages which were rapidly organized without significant distortion of the liver structure. Fatty change induced by a high fat diet was recognized in cytological smears stained with Fettrot 7B, and its progression with time monitored. The cytologie findings correlated well with histopathological and biochemical changes observed in the same animals.