One hundred and fifteen patients from 5 general practices participated in a 12-week, double-blind study comparing L-tryptophan, amitriptyline, L-tryptophan-amitriptyline combination and placebo in the treatment of depression. Analysis of total score on the Hamilton Depression Scale and a global rating of depression showed that all 3 active treatments were more effective than placebo. Significantly more patients were withdrawn as treatment failures in the placebo group compared with the active treatment groups. Side-effects necessitated withdrawal of more patients from the amitriptyline group than from the other active treatment groups, but this difference was not significant. Plasma amitriptyline and nortriptyline levels were similar in the amitriptyline and combined treatment groups. Standard haematological and biochemical profiles did not alter significantly in any group, but mean heart rate was significantly increased in patients receiving amitriptyline. There was no change in free or total plasma tryptophan concentration with treatment or on remission of symptoms.