Disuse atrophy of skeletal muscle is a phenomenon commonly associated with prolonged periods of inactivity resulting in reduced cross sectional area of the myofibres. Satellite cells are mononucleated cells closely juxtaposed to myofibres that are required for the repair and hypertrophy of skeletal muscle (Adams, 2006). In humans, the number of myofibre associated satellite cells can change, increasing following resistance training and decreasing following a period of detraining (Kadi et al., 2004). However, the association between disuse atrophy and satellite cell number has not been closely investigated. We aimed to determine whether atrophy associated with long term disuse leads to loss of satellite cells. Following local anaesthesia (2% lignocaine), needle biopsies were taken from the left and right vastus lateralis muscles of a young male volunteer (aged 25 yrs) who had suffered a knee injury six years prior. Visible connective and adipose tissue were dissected and the biopsies split into two parts, one for histology to determine muscle fibre composition and fibre size and one for satellite cell isolation. For histological analyses, the tissue was mounted in OCT medium, and frozen in iso-pentane cooled to -80°C. Serial cross-sections (10μm) were cut and ATPase histochemistry was performed for the determination of type I and II fibre size and relative composition. Rather than counting a limited number of satellite cells in cryosections, we aimed to measure all satellite cells by extracting them from the biopsy sample. For satellite cell isolation, tissue was weighed and digested in a solution containing trypsin (5mg/ml). Cells were harvested by centrifugation and cultured in skeletal muscle cell growth medium supplemented with 10% foetal calf serum. After 10 days the total number of cells was counted. The proportion of muscles cells was determined by expression of desmin using immunofluorescence. The mean fibre area of Type I and II fibres was 5206 (3377-7361)μm2 and 6248 (4430-7449)μm2 respectively in the uninjured leg, but were on average 16% and 32% lower in the injured leg. The proportion of Type II fibres was slightly higher (60%) in the injured verus the uninjured (54%) leg. The total yield of cells extracted from muscle tissue was 9834 cells/mg in the uninjured versus 7081 cells/mg in the injured leg. The proportion of desmin positive cells in the extracts was 97% in the uninjured and 89% in the injured leg. The data suggests that there is a concurrent loss of satellite cells with the reduction in myofibre area.