The purpose of this paper is to present the changes that take place in testicular microcirculation measured by DLF during systemic administration of LHRH agonists. The essay includes a comparison with the variations registered in the volume of testicular interstitial fluid, the anatomopathological changes and the associated leucocyte demyeloperoxidase levels. We also examine the relationship between testicular microcirculation changes and plasma testosterone levels. To do this, 50 male Wistar rats were randomly divided into 5 groups, using 10 as control group and the remaining 40 distributed in 4 groups. Measurements were done at 2, 4, 8 and 24 hours after administration of Tryptorelin 0.4 mg i.v. We found that acute administration of an LHRH agonist causes a series of significant changes on testicular microcirculation. Testicular rhythmic microcirculatory flow, i.e., vasomotion, disappears. In turn, accumulation of PMN leucocytes associated to increased venular permeability takes places. Such pre- and postcapillary vascular changes lead to increased vascular permeability which results in increased volume of testicular interstitial fluid. This increased capillary permeability is responsible for the extensive interstitial oedema that would explain the serious histological changes seen on the seminiferous tubule with these drugs.