Many studies have reported correlations between measures of aggression and
indices of serotonergic function, but most have studied patient or offender
populations and relatively few have investigated plasma concentrations of
the serotonin precursor tryptophan. This study investigates the relationshi
p between plasma concentrations of tryptophan and trait hostility depressio
n and anxiety in male healthy volunteers. Sixty-seven healthy male voluntee
rs gave blood samples and completed trait questionnaires. Plasma tryptophan
was positively correlated with the Buss-Durkee Hostility Inventory Total s
core and Motor Aggression subscale, but not with the Attitudinal Hostility
subscale or with trait anxiety or depression. In conclusion, there is evide
nce for an association between high concentrations of plasma tryptophan and
aggressive behaviour in men, presumably mediated by some aspect of central
serotonergic function, which seems unlikely to be explained by high trait
anxiety or depression.