Our current knowledge of the neurobiology of romantic love remains scanty. In view of the complexity of a sentiment like love, it would not be surprising that a diversity of biochemical mechanisms could be involved in the mood changes of the initial stage of a romance. In the present study, we have examined whether the early romantic phase of a loving relationship could be associated with alterations in circulating levels of neurotrophins (NTs). Plasma levels of NGF, BDNF, NT-3 and NT-4 were measured in a total of 58 subjects who had recently fallen in love and compared with those of two control groups, consisting of subjects who were either single or were already engaged in a long-lasting relationship. NGF level was significantly higher (p < 0.001) in the subjects in love [mean (SEM): 227 (14) pg/ml] than in either the subjects with a long-lasting relationship [123 (10) pg/ml] or the subjects with no relationship [149 (12) pg/ml]. Notably, there was also a significant positive correlation between levels of NGF and the intensity of romantic love as assessed with the passionate love scale (r = 0.34; p = 0.007). No differences in the concentrations of other NTs were detected. In 39 subjects in love who-after 12-24 months-maintained the same relationship but were no longer in the same mental state to which they had referred during the initial evaluation, plasma NGF levels decreased and became indistinguishable from those of the control groups. Taken together, these findings suggest that some behavioural and/or psychological features associated with falling in love could be related to raised NGF levels in the bloodstream.