In this paper, we develop a machine repair model with reneging for (m, M) system wherein the system will fail when all spares are being used and there are less than m machines in the system. In case all repairmen are busy, the repair rates of failed machines are assumed to be faster than the situation when, at least one repairman is free. The transient analysis has been provided by solving a set of linear equations in terms of Laplace transform of the state probabilities. Expressions for the system reliability and the mean time-to-system failure (MTSF) are derived in terms of state probabilities. Numerical results are also carried out to examine the effect of various parameters on the system reliability and mean time-to-system failure.