In guinea pigs, it is assumed that ovulation in the oestrous cycle occurs spontaneously. However, observations of mating of wild cavies (Cavia aperea) suggest that ovulation is induced by the presence of males. This diploma thesis investigated whether the females ovulate spontaneously or ovulation is induced by presence of males. Females of C. aperea were divided into two groups. One group had no contact with males (n = 8) and the other (n =8) was able to interact with the males through mesh wire. The aim of this study was to compare the oestrous cycles of both groups. Over a period of 39 days daily vaginal smears were collected and microscopically evaluated after staining. In parallel, faecal oestrogen metabolites were determined by enzyme immunoassay. Likewise, the vulva and the opening of the vaginal closure membrane were evaluated daily. The oestrous cycle of females in both group was 16 days on average. Analyses of data (the number of cornified cells, the concentration of oestrogen and the number of openings of the vaginal closure membrane) found no significant difference between the two groups. These results suggests that the oestrous cycle of C. Aperea is not affected by the presence of males. During investigation only a weak correlation has been observed between the observation of the vaginal closure membrane and the cytological results. Thus for reliable determination of ovulation, the observation of the opening of the vaginal closure membrane should always be combined with the results of a vaginal smear. Unfortunately the results of the oestrogen analysis had weak correlation with results from vaginal cytology. To characterize the wild cavy ´s oestrous cycle precisely, further studies focusing on relation between the levels of oestrogen and progesterone metabolites in faeces and results of the vaginal smear tests are recommended.