Neural cell adhesion molecule (N-CAM) and the paired box transcription factor, Pax-7, are both known to be markers of myogenesis. While N-CAM expression in human muscle has been well documented, few studies have investigated the expression of Pax-7. The aim of this study was to identify the immunoreactivity of these two satellite cell markers after a single bout of exhaustive eccentric exercise. Eight untrained males (22-27yrs) performed 210 maximum eccentric contractions in an isokinetic dynamometer. One leg was exercised involuntarily using electrical stimulation (ES), while the contralateral leg was exercised voluntarily (VOL). Muscle biopsies of the vastus lateralis muscle were taken from both legs on day 0 and 8 after the exercise bout. Serial sections were immunohistochemically stained for N-Cam and Pax-7. The percentage of N-CAM and Pax-7 positive cells was calculated as the number of positive cells/(positive cells + myonuclear number) x 100. Numerical data is shown as the mean ± standard deviation and a student’s t-test was used to determine statistical significance. Myofibre necrosis was found in the vastus lateralis muscle of the ES leg only with a significant increase in desmin negative cells: Day 0 (0 ± 0%) and day 8 (13.7 ± 12.0%; p<0.05) and a corresponding inflammatory cell infiltration into the necrotic myofibres. No change above baseline was found in the VOL leg. The ES leg also showed a significant increase in N-CAM expression over time (Day 0: 2.48 ± 0.69%; Day 8: 22.53 ± 17.46%, p<0.05) and when compared to the VOL leg (Day 0: 2.42 ± 0.69%; Day 8: 5.26 ± 2.17%, p<0.05). Pax-7 immunoreactivity increased significantly over time in the ES leg (Day 0: 3.34 ± 1.56%; Day 8: 9.38 ± 6.24%*, *p<0.05) and when compared to the VOL leg (Day 0: 3.13 ± 1.81%; Day 8: 2.66 ± 2.19%). The pattern of expression of the N-CAM and Pax-7 was dissimilar. In particular, the Pax-7 expression 8 days after the exercise bout was markedly less than N-CAM expression. It has recently been reported that PAX-7 expression is not found in freshly regenerating myotubes or in presumed myoblasts. Additionally, Pax-7 expression remains low or undetectable at the proliferative myoblast stage but becomes prominent in an increasing proportion of mononucleate cells after the induction of differentiation (Reimann et al., 2004). We have previously hypothesised that after a single bout of exhaustive eccentric exercise there is a proliferation of satellite cells that do not undergo terminal differentiation unless an additional bout of exercise is undertaken (Crameri et al., 2004). This study suggests that the N-CAM positive cells at day 8 are satellite cells that have undergone proliferation but have not undergone terminal differentiation.