Guar gum is a dietary fibre advocated for use in lowering serum total cholesterol levels in patients with hypercholesterolaemia. Its mechanism of action is proposed to be similar to that of the bile-sequestering resins. Although guar gum is also employed as an adjunct in non-insulin-dependent diabetic patients this review is restricted to its efficacy as a hypolipidaemic agent. Clinical trials indicate that, when used alone, guar gum may reduce serum total cholesterol by 10 to 15%, although some studies show no significant response. An attenuation of this effect during longer term treatment has been seen but evidence of this effect is equivocal. As an adjunct to established therapies (bezafibrate, lovastatin or gemfibrozil) guar gum has shown some promise: it may produce a further reduction in total cholesterol of about 10% in patients not responding adequately to these drugs alone. Gastrointestinal effects, notably flatulence, occur relatively frequently and may be considered unacceptable by some patients. Standardization of formulations and methods of administration of guar gum is required to clarify its pharmacological and clinical properties. Thus, on the basis of presently available evidence guar gum as monotherapy may be considered at most modestly effective in reducing serum cholesterol levels. Nonetheless, further investigation of guar gum is warranted, particularly its use as an adjunct to produce additional reductions in serum cholesterol in patients not responding optimally to other lipid-lowering agents.