Investigation of possible effects of tomato juice on adenosine deaminase (ADA) activity in prostate tissue from cancer patients was aimed in this study. Ten prostate tissues from patients with pathologically proven localised prostate cancer (Gleason scores 4 to 7) were used in the study. In the tissues, ADA activities with and without preincubation with different amounts of tomato juice were performed. Tomato juice causes significant inhibition on ADA activity in the prostate tissues. Protective effect proposed for tomato against prostate cancer may result from its inhibition potential on ADA. (C) 2003 Elsevier Inc. All rights reserved.