A longitudinal investigation which was principally exploratory in nature was undertaken in order to elucidate the interrelationships among several factors associated with development in the first year. Ten full term appropriate-weight, fourteen preterm appropriate-weight for dates, and ten full term small-for-dates (SFD) infants, and their mothers were assessed in the areas of sleep state organisation, maternal perception of her neonate, mother-infant interaction patterns at two, three, and six months, developmental status at four and ten months, and perceived infant temperament at six months. The implications of state variables were focussed on in regard to interaction and developmental status. Both preterm and SFD infants were disorganised in their sleep states and in comparatively their waking states until three months, with state instability persisting to six months in the SFD group. Sleep state stability predicted ten-month development in full term and preterm infants, waking active stage levels at two and three months were predictive in SFD infants. Preterm and SFD infants scored lower than full term infants on MDI assessments at four and ten months; maternal stimulation was negatively related to development in the preterm group and positively related in the full term group, supporting previous suggestions that preterm infants have a low threshold for. overstimulation. There was a negative relationship in the SFD infants between ten-month development and variables reflecting early infant activity. SFD dyads were remarkably inflexible in their interaction patterns from two to six months, and perceived infant temperament was strongly related to ten-month development. The findings document striking differences in the course of development in the first year for the three kinds of infants. The importance of considering state related variables is underscored, and the differential effects of stimulation, maternal perception, perceived temperament, and infant neonatal status on the underlying processes of development are demonstrated