The therapeutic response to L-5HTP, a serotonin precursor, was studied in an attempt to identify clinical subgroups of primary headache patients. The results at the 4th month control in 100 patients under L-5HTP treatment at the dose of 300 mg/day confirm previous observations on the activity profile of the drug, the effects of which are equally distributed between recurrent and daily forms as well as among clinical subtypes. The emerging profile of the responsive patients is characterized by such peculiar traits as prevalence of previous major mood disturbances and minor frequency of anxiety, longer duration of the illness and higher occurrence of some associated symptoms, lower incidence of exogenous and hormonal trigger factors, and previously positive response to pizotifen treatment.