The commonly used age dependent preventive maintenance policies, for a repairable system, are based on the minimal repair model. But proportional hazards model (Cox, 1972; Lawless, 1987) is another reasonable model which will account for the possibility of additional damage at failures. Therefore, a test designed to discriminate between these two models will be useful. Such a test is developed and presented here. This test will be applicable when a large number of system copies, experiencing only a few failures each, are available for analysis. Initially, the score test is proposed under the assumption of known baseline rate of occurrence of failures of the system. Later this assumption is relaxed. The problem is then formulated in the framework of marked point processes. Tests based on partial likelihood are constructed. Further, a martingale estimator of the integrated baseline intensity is suggested. Performance of the tests is investigated by computing empirical powers for samples of sizes 50, 75 and 100