During routine grooming, cats normally ingest large quantities of hair. The hair may conglomerate into solid masses in the gastrointestinal tract, thus causing the formation of hairballs (trichobezoars). In the most cases this hair may be passed in the faeces or may be vomited. When hair is retained in the gastrointestinal tract, this can cause digestive disorders.Cats are eating instinctively grass halms to stimulate vomiting. Nowadays the food industry offers various kinds of pastes, pills or feeds for helping to avoidthe formation of hairballs.The objective of our study is to test a newly developed diet, which should improve the excretion of ingested hairs.Twelve cats from the University of Veterinary Medicine Vienna were divided into two groups.The test was arranged as a cross-over-study. At first six from the twelve cats received the diet during a period of nine days. At this time the faeces of all cats were collected daily. After a break of one week, the two groups were switched.All cats had no problem to eat their diet.By the majority of the cats was presented an optimal faecal quality either with or without diet.The comparison of the average value of the amount of hair in the faeces showed that there was no difference either with or without diet.The trichobezoars were classified by length into small (= 2 cm), medium (2,1 -5 cm) and large hairballs (> 5 cm).The respective sum of the hair length was quantifiered by a factor.Our hypothesis could not be confirmed. In conclusion the number of large trichobezoarswas not reduced by the diet and the number of small trichobezoars was not increased.