An increasing proportion of the population perceive complementary medicine as a safer alternative for non-life threatening conditions such as genital herpes. The extract of the plant Echinacea purpurea (Echinaforce) has been shown to have immunomodulating properties and has been advocated in the lay press for the treatment of genital herpes. This study, a single centre, prospective, double blind, placebo-controlled cross-over trial set out to assess whether an extract of the plant and root of E. purpurea can prevent or decrease the frequency and severity of genital herpes recurrences. These were assessed using a detailed history and clinical review of symptoms. Visual analogue scales were used for documentation and haematological and immunological parameters were measured. Over a one-year period, 50 patients took part in the study receiving 6 months' placebo and 6 months' Echinaforce each. No statistically significant benefit could be detected in this study comparing placebo versus Echinaforce in the treatment of frequently recurrent genital herpes.