The functional, nutritional and medicinal components of mushrooms have been the subject of intense research. Many mushrooms have been reported as therapeutic foods, useful in the prevention of diseases such as hypertension, diabetes, hypercholerostemy, atherosclerosis and cancer. From the about 2000 species of edible mushrooms, less than 25 are amply used as food. The mushrooms have generally been considered functional foods and, consequently, important sources of bioactive compounds, the β-glucans, terpenes, phenolics and steroids being so far the most important. These compounds are said to exert several effects, the most prominent being the antitumoral, antimutagenic, anticytotoxic, antimicrobial, antioxidant, hepatoprotective, antiinflammatory, hypoglycemic and anti-dislipidemic actions. Presently there is intense research worldwide attempting to quantify and characterize these effects using either semi-purified preparations or purified compounds. The present review presents basic information about the functional, nutritional and medicinal components of mushrooms and discusses possible strategies for improving the efficiency of the investigations. Research on this subject will be more adequate and useful if it is conducted  systematically using always the same standardized products. Cooperation between laboratories with different skills is suggested as a means of producing more reliable and meaningful results.