There is good evidence from in vitro studies that Camellia sinensis (green tea) catechins have a role in protection against degenerative diseases. However, the concentrations used in vitro are often higher than those found in animal or human plasma, and so in vivo evidence is required to demonstrate any protective effect of catechins. This article summarises the most interesting in vivo animal studies on the protective effects of C. sinensis catechins against biomarkers for cancer, cardiovascular disease and other degenerative diseases. Generally, most studies using animal models show that consumption of Cannabis sinensis (catechins) provides some protection, although most studies have not examined dose response. C. sinensis catechins could act as antitumourigenic agents and as immune modulators in immunodysfunction caused by transplanted tumours or by carcinogen treatment. C. sinensis has antiproliferative activity in hepatoma cells and hypolipidemic activity in hepatoma-treated rats, and some studies report that it prevents hepatoxicity. It could act as a preventive agent against mammary cancer post-initiation. Nevertheless, the implications of C. sinensis catechins in preventing metastasis have not been clearly established. Long-term feeding of C. sinensis catechins could be beneficial for the suppression of high-fat diet-induced obesity by modulating lipid metabolism, could have a beneficial effect against lipid and glucose metabolism disorders implicated in type 2 diabetes and could also reduce the risk of coronary disease. Further investigations on mechanisms, the nature of the active compounds and appropriate dose levels are needed.