Fathers in two-parent families are becoming increasingly involved in infant care, highlighting the need to understand the determinants and influence of father-infant interactions. Paternal responsiveness is a core component of positive father-infant interactions. This study investigated associations between paternal responsiveness and infant development; and paternal low mood and paternal responsiveness. Participants were a sub-sample of father-infant dyads (n=47) from a UK community cohort study: The Avon Longitudinal Study of Parents and Children. The Mellow Parenting Coding System was used to measure paternal responsiveness within a video-recorded father-infant interaction at 12 months. Infant development was assessed using the Griffiths scales at 18 months and paternal low mood was measured using the Edinburgh Post-Natal Depression Scale (EPDS) at 8 months. Linear regression analysis provided no evidence for an association between paternal responsiveness and infant development. Due to methodological limitations it is unclear whether this reflects a true null relationship. Unexpectedly, lower paternal mood (indicated by higher scores on the EPDS), was found to be associated with greater paternal responsiveness. For every standard deviation increase in EPDS score, fathers displayed approximately two additional responsiveness behaviours per minute in the observed interaction; this corresponds to a standardised effect size of 0.32 standard deviations. The mechanisms for this association are unclear, but possibilities are discussed. The finding requires replication within larger studies, but clinicians may wish to consider that fathers who achieve very low scores on measures of depressed mood may be at risk for low paternal responsiveness.