Latent antithrombin (L-AT), a heat-denatured form of native antithrombin (AT), is a potent inhibitor of pathological tumor angiogenesis. In the present study, we have investigated whether L-AT has comparable antiangiogenic effects on physiological angiogenesis of ovarian tissue. For this purpose, preovulatory follicles of Syrian golden hamsters were mechanically isolated and transplanted into dorsal skinfold chambers chronically implanted in L-AT- or AT-treated hamsters. Non-treated animals served as controls. Over 14 days after transplantation neovascularization of the follicular grafts was assessed in vivo by quantitative analysis of the newly developed microvascular network, its microvessel density, the diameter of the microvessels, their red blood cell velocity and volumetric blood flow as well as leukocyte-endothelial cell interaction using fluorescence microscopic techniques. In each group, all of the grafted follicles were able to induce angiogenesis. At day 3 after transplantation, sinusoidal sacculations and capillary sprouts could be observed, finally developing complete glomerulum-like microvascular networks within 5 to 7 days. Overall revascularization of grafted follicles did not differ between the groups studied. Interestingly, follicular grafts in L-AT- and AT-treated hamsters presented with higher values of microvessel diameters and volumetric blood flow, when compared to non-treated controls, which may be best interpreted as a reactive response to an increased release of vasoactive mediators. In conclusion, the present study demonstrates, that L-AT has no adverse effects on physiological angiogenesis of freely transplanted ovarian follicles. Thus, L-AT may be an effective drug in tumor therapy, which blocks tumor growth by selective suppression of tumor vascularization without affecting new vessel formation in the female reproductive system.