Abstract: Trichobezoars (TCBs) are an affliction of domesticated cats; they rarely are fatal but can cause undesirable social behavior. Bromelain, a cysteine protease found naturally in pineapple juice, has been suggested as a practical dietary treatment, but there are few data on its activity. Little is known about the chemical composition of TCBs; such data are needed in developing a treatment. Samples of TCBs and hair were obtained from cats in a commercial facility and analysed for amino acids and total protein concentrations. Amino acid concentrations varied dramatically among TCBs but not among hair samples, suggesting that the proportions of hair and non-hair components varied markedly among TCBs. TCBs were estimated to contain 42% hair on average, but there was substantial variation among samples. Bromelain was able to degrade N in TCBs more effectively at a pH of 7.0 than at a pH of 2.5, but differences were not large (37 at pH of 7.0 vs. 26 % at 2.5). Some TCBs were degraded less than 10%, while others were degraded more than 50%; the variation probably reflected amount of non-hair material. While bromelain did not degrade TCBs extensively or consistently; the degradation that did occur probably was sufficient to disrupt the structure of TCBs and promote passage. Testing is needed to establish in vivo efficacy.