Phospholipase A2 are enzymes that hydrolyse phospholipids at the sn-2 position. The catalytic reaction leads to the generation of a free fatty acid and a lysophospholipid. Both of these products are involved in second messenger activities in the cell. There are several distinct PLA2s, most of them are regulated by Ca2+. The calcium-independent PLA2s (iPLA2) do not require Ca2+ for their activity and additionally do not show substrate specificity, like most of the PLA2s. Therefore they have been suggested mainly to have housekeeping function in the cell and do not contribute as regulatory proteins.In bone cells the involvement of PLA2s in the regulatory processes leading to arachidonate release have been described, but not for iPLA2. This master thesis aimed at establishing a method, based on the catalytic turnover of a radio labelled phosphatidylcholine, to measure iPLA2 activity in osteoblastic cells. The iPLA2 assay was established to specifically measure iPLA2 under the chosen conditions (Ca2+ free) according to the procedure of Yang et al. It was further modified for the measurement of osteoblastic cell lines to be able to distinguish between cytosolic (iPLA2?) and membrane-bound (iPLA2?) derived enzyme activity. Evaluation of the assay included reproducibility, sample treatment, time course experiments and sample stability. Reproducibility of the assay within one set of experiments was found to be <5%, larger variations were found for day to day reproducibility. The specificity of the measured iPLA2 activity was evaluated by the use of BEL, a specific iPLA2 inhibitor. Western blot analysis for iPLA2? was performed to assign measured activities to iPLA2 ? and iPLA2 ?, respectively.In the course of this thesis iPLA2 activity in osteoblasts has been measured and described for the first time. Moreover, the presence of both, iPLA2? and iPLA2? activity was demonstrated.