Weather anomalies are the cause of the more and more frequent occurrence of the rezorcycyklic acid derivatives--zearalenone--in the fodders of the animal origin. This mycotoxine induces in the organism of gilts an oestrus-like condition. According to the latest reports the zearalenone derivatives were found in the human food-stuffs in the retail market. It was considered important to assay the concentration of zearalenone and its derivatives in the standard and therapeutic feeds for dogs. Zearalenone and its derivatives were found in 48 commercial formulations for a total number of 57 brands analysed.