Bovine mammillitis has been sporadically observed among cattle in Japan. Since parapoxvirus (PPV) and bovine herpesvirus type 2 (BHV-2) were suspected as agents of the diseases, specific and sensitive methods for diagnosis of these diseases were studied. Seroepidemiological surveys were performed on PPV by agar gel immunodiffusion test and ELISA using protein AG, and on BHV-2 by virus neutralization tests. Serum samples were collected from cattle in various parts of Japan. Positive reactors to PPV were found all over Japan and the rate of positive reactors was more than 70%. On the other hand, reactors to BHV-2 were found sporadically and their positive rate was about 1%. Positive reactors to PPV were observed in Japanese serow, suggesting that PPV is transmitted between domestic and wild animals. Genetical diagnosis methods by PCR were developed for the detection of PPV and BHV-2, and their practical use was evaluated. Semi-nested PCR was applied to the diagnosis of PPV infection and it was able to detect viral DNA from lesions of clinically affected animals in the fields. The reaction was effective for all PPV strains and these were divided into 4 groups by restriction fragment length polymorphism. Shuttle PCR was developed for diagnosis of BHV-2 infection and the specificity and sensitivity of the reaction were confirmed by digestion with restriction endonuclease AulI and by using homogenized muscle and skin of mice experimentally infected with BHV-2.