We consider N unreliable machines that are maintained by M repairmen. The time until failure of machine i, and its repair by repairman j, are exponentially distributed random variable with parameters λi, and μj, respectively. All failure times and repair times are independent. Machine i earns ci, per unit time, while it is working. We wish to maximize the expected total discounted reward. It is shown that when the following conditions are satisfied — c1 ≥ … ≥ cN and c1/λ1≥…≥cN/λN, the policy that assigns the fastest repairman to the machine with the lowest index is optimal. Moreover, it is shown that when the second condition is replaced by λ≤ … ≤λN, then this policy maximizes, stochastically, the number of the most reliable machines at every time t.