Background: The etiology of celiac disease (CD) is related to undigested fragments of gluten and gliadin which damage the small bowel. Mucosal enzyme deficiency is an important factor in CD pathology. A clinical trial has shown that the effects of a gluten challenge to patients with CD could be ameliorated by the use of an enzyme supplement. Objective: Enzyme therapy using enterically coated tablets containing caricain (Gluteguard) was investigated as a means of protecting patients with CD against wheat gluten. Methods: A randomized placebo-controlled trial was carried out on 20 CD patients in clinical remission. The patients were divided into a group of 14 given Gluteguard and a group of 6 given a placebo daily. Both groups were given a challenge of 1g of gluten daily. Symptoms were graded and recorded over a period of 42 days. Duodenal tissue was taken at the beginning and end of this period, together with blood for assay of tissue transglutaminase (tTG-IgA) antibodies. Results: The results showed that oral enzyme therapy based on caricain, was effective in ameliorating the symptoms of CD giving a statistically significant difference between treatment and placebo (P<0.01) after 14 days challenge. General well-being was also improved from 6.1 to 8.4 (P< 0.01) by the enzyme therapy. Four of the six placebo group patients (67%) and one of the 14 treatment patients (7%) to withdraw from gluten challenge after 14 days due to development of serious symptoms. The difference between the groups was significant (p < 0.001). For the per protocol patients on Gluteguard therapy, there were no significant changes in markers of histological damage or biopsy results after 42 days of gluten challenge. Conclusions: This study demonstrated that oral anti-gluten enzyme therapy using Gluteguard was able to significantly protect celiac patients from adverse symptoms being induced by gluten challenge. Furthermore, mucosal damage was not exacerbated in patients taking Gluteguard along with their daily gluten challenge, suggesting that the enzyme tablets may also help with the recovery of epithelium in the longer term. Availability of a preventative enzyme treatment like Gluteguard will likely add to the quality of life and well-being of coeliac patients, especially those who have difficulty in strictly adhering to a gluten-free diet