Stem cell techniques have facilitated a number of potential uses for such cells in cell therapy and drug development. Studies of the cAMP/protein kinase A (PKA) pathway are widely employed to investigate the effects of a large variety of substances. We assayed the cAMP pathway in human skin-derived mesenchymal stem cells (S-MSC) to evaluate donor to donor variations in response to pharmacological manipulations in vitro. Immunophenotyping of S-MSC revealed that, in general, 95% of S-MSCs were positive for CD90, CD73 and CD105 and negative for the expression of haemopoetic markers CD14, CD45 and human leukocyte antigen-DR (HLA-DR). Nevertheless, fluctuations occurred in basal cAMP levels from 5 pmol/mg to 18 pmol/mg. Total cAMP response element binding protein (CREB) concentrations ranged from 0.8 ng/ml to 1 ng/ml, whereas the proportions of phospho-CREB versus total CREB differed between the cell lines. Basic fibroblast growth factor (FGF-2) and epidermal growth factor (EGF) stimulated cAMP generation, whereas leukaemia inhibiting factor reduced some of their effects. Forskolin (0.05 and 1 mM) acted in synergy with FGF-2 and EGF; however, it caused pronounced donor to donor differences in the increase of cAMP and phospho-CREB levels. Additionally, dibutyryl-cAMP caused significant donor to donor variations in cell proliferation, possibly indicating a change of cell differentiation status. We speculate that similar donor diversity might be observed after cell stimulation with various G(s)-protein-coupled receptor ligands. Heterogeneity of donor cell responses to stimulation of the cAMP pathway indicates the need for wide safety margins for S-MSC use in drug screening; nevertheless, knowledge of this heterogeneity might be useful for the design of donor-specific cell therapy.