We use an in-vitro osteoblast cell culture model to investigate the effects of low-frequency (7.5 Hz) pulsed electromagnetic field (PEMF) stimulation on osteoblast population, cytokines (prostaglandin E(2) (PGE(2)), transforming growth factor beta1(TGFbeta1), and alkaline phosphatase (ALP) activity to find the optimal intensity of PEMF for osteoblast growth. The results demonstrate that PEMF can stimulate osteoblast growth, release of TGFbeta1, and, in addition, an increase of ALP activity. The synthesis and release of PGE(2) in the culture medium are reduced with increasing numbers of cells. Higher intensity does not necessarily mean increased osteoblast growth, and the most efficient intensity is about 2 mV/cm in this case. Although the lower intensities of the PEMF are yet to be determined, the results of this study can shed light on the mechanisms of PEMF stimulation on non union fracture therapy and osteoporosis prevention in the future.