Hypericum species are widely used plants in folk medicine and. presently are the subject of many clinical trials concerning their antidepressant and anti-retroviral activities, including anti-HIV effects. An analytical study of methanolic extracts of thirteen portuguese Hypericum species was carried out. An HPLC method was used for the detection and quantification of important biologically active phenolic compounds present in Hypericum species, such as hypericin, quercetin, quercitrin, isoquercitrin, rutin, hyperoside, kaempferol, amentoflavone, caffeic acid and chlorogenic acid. The study is believed to be useful in assessing potential therapeutical activities of all continental portuguese Hypericum species, since the results demonstrate significant differences of composition among them.