The progressive and regressive stages of fibropapilloma in their unusual papillomatous formation in calves are described. Papillated hyperplasia of the epidermis and high mitotic activity in stratum basale characterized the progressive stage. The regressive stage (120 days later) showed infiltration of dermal papillary layer by mononuclear cells (CD3+ cells and macrophages). a thin stratum spinosum without long rete ridges. and massive hyalinization of collagen in the dermis. Several basal cells in the mitotic cycle were immunohistochemically positive for papilloma virus. Immunohistochemically, papilloma virus was demonstrated in these lesions with the higher numbers of virus positive cells in the progressive stage. Some cells in the stratum spinosum showed both cytoplasmic-and nuclear-staining for the virus. which implies the budding of the virion into the cytoplasm in these layers. Boville papillomatosis. immunohistochemistry. CD3 lymphocytesPapillomatosis of papilloma-viral aetiology is a benign epithelial neoplasm with (fibropapilloma) or without (papilloma) connective tissue proliferation. Six different types of bovine papilloma virus have been identified as BPV -1 -BPV -6 (J arre t et al. 1984) and classified into subgroups A and B. Subgroup A viruses cause skin fibropapillomas subgroup B viruses cause true epithelial papillomas.BPV -2 infects traumatized skin and lasts about a year including an initial month oflatency and a final 2 months of tumour rejection. Tumour development can be divided into the following four stages (Campo 1995): fibroma with active proliferation of dermal fibroblasts, fibroma with acanthosis, true fibropapilloma, and tumour regression. Tumour regression is probably mediated via cellular immunity because humoral immunity is not effective in initiating tumour regression (J ablonska 1982).The aim of this paper is to describe the progressive and regressive stages of bovine papillomatosis in its unusual papillomatous formation recorded in the SpiS region (Slovak Republic). In addition, the study deals with the reaction of immunocompetent cells in infected tissue and the participation of CD3 cells in tissue reaction. Materials and Methods AnimalsSkin papillomas naturally developed in 5 young calves (1-2 years old) were included into this study. Samples of fibropapilloma were excised twice in the span of 120 d of growth. Processing of histological materialThe samples were processed using a standard procedure i.e. fixed in 10% neutral formalin. and embedded in paraftin. Sections of a thickness of 5-6 11m were stained with haematoxylin -eosin.

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