Reactivity to an aversive tactile stimulus was assessed in 114 fullterm and 163 preterm infants. Irritability and activity, two components of temperament, were rated during a 5-s application of a cold disc on the thigh and for 5 s following the trial. Patterns of reactivity were observed for fullterm females and males and preterm females where irritability increased and activity decreased across 5 trials. Females were more irritable than males during stimulation, and fullterm infants were more active than preterm infants on the initial trial. Implications of term and sex differences for early integrity are discussed.