Social attachment is fundamental for its relevant impact upon survival and reproduction in several animals and particularly so in humans. Recently, much research efforts have been directed towards the understanding of the neurobiological basis of social attachment. Besides oxytocin, vasopressin and specific brain areas, it has also been suggested that neurotrophins (NTs) might be involved. NTs are a family of structurally similar proteins including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) amongst others, which play an important role in the survival, differentiation and functioning of neurons (Patapoutian & Reichardt, 2001). Preclinical studies suggest that BDNF might be involved in hippocampal degeneration (Duman et al. 1997) following different stressors, such as maternal deprivation (Meaney, 2001). The BDNF changes would render adult animals more vulnerable to exaggerated stress responses and anxious behaviours (Ladd et al. 2004). These findings suggest that BDNF, and perhaps all NTs, might act as mediators to translate the effects of environmental stimuli on the development of the ‘ social brain’. A type of social attachment that seems to be peculiar to humans is the so-called ‘romantic attachment’, which is the establishment of a relationship between two sexual partners (Hazan & Shaver, 1987). Given the lack of information on this topic, we explored the possible relationship between BDNF plasma levels and romantic attachment, as assessed by the Experiences in Close Relationships (ECR) questionnaire (Brennan et al. 1998), a self-report instrument for measuring romantic attachment in adults.