Ageing is characterised by a loss of muscle mass (sarcopenia). The mechanisms contributing to this loss are not known. One theory is that sarcopenia results from an impaired response to contraction-induced injury. In rodent muscle, evidence suggests that changes in circulatory factors contribute to the decline in regenerative capacity, since the % of desmin (a muscle cell marker) is lower in primary cells cultured in serum from old animals (1). The aim of this study was to assess the myogenicity of human satellite cells cultured in serum from young or old people. Needle biopsies were taken (under local anaesthetic: 1% Lignocaine) from the vastus lateralis muscle of a young (aged 23 yrs) and an older (aged 65 yrs) female subject. Serum was obtained from 8 young (aged 23-36 yrs) and 8 elderly (aged 65-82 yrs) subjects (4 male and 4 female per group). The tissue was digested with trypsin and the resulting cell supernatant was cultured in a humidified incubator at 37°C and 6% CO₂ in skeletal muscle cell growth medium (SMCGM, Promocell, Germany) supplemented with 10% foetal calf serum. Cells were plated at a density of 1250/well in 96 well dishes. After 24 hours the SMCGM was replaced with skeletal muscle cell basal medium (Promocell) which was supplemented with 15% human serum. Cells were fixed after 46 hours in 4% paraformaldehyde + 0.2% triton. Immunocytochemistry was performed using mouse monoclonal antibody against desmin (D33, Santa Cruz) and a rabbit anti-mouse secondary antibody conjugated to Alexa Fluor 488 (Invitrogen). The nuclei were counterstained with Hoechst 33258. Analysis was performed using a Zeiss Axiovert fluorescence microscope. Myogenicity was defined as the percentage of the proliferating cells expressing desmin. Two wells were studied per condition and the mean value used for analysis. At least 500 cells per well were counted. Satellite cells from the elderly subject showed no difference (unpaired t-test) in myogenicity when cultured in either young serum (24.9±3.9%, mean±SEM) or old serum (26.6±3.6%). Although myogenicity of cultures from the young subject was consistently higher, the age of serum also had no effect (41.6±4.1%, versus 42.3±4.0% for young and old serum respectively). The data suggest that in contrast to studies on mice, factors in the aged human circulation do not appear to affect the myogenicity of human primary muscle cells.