During bone remodelling bone is resorbed by osteoclasts and replaced again by osteoblasts through the process of bone formation. Clinical trials and in vivo animal studies suggest that specific polyunsaturated fatty acids (PUFAs) might benefit bone health. As the number of functional osteoblasts is important for bone formation the effects of specific PUFAs on in vitro osteoblastic cell proliferation were investigated. Morphological studies were conducted to determine whether exposure of the cells to these agents caused structural damage to the cells thereby yielding invalid results. Results from this study showed that arachidonic acid (AA) and docosahexaenoic acid (DHA) both inhibit cell growth significantly at high concentrations. The anti-mitotic effect of AA is possibly independent of PGE(2) production, as PGE(2) per se had little effect on proliferation. Further study is required to determine whether reduced proliferation due to fatty acids could be due to increased differentiation of osteoblasts to the mature mineralising osteoblastic phenotype.