Skin conductance shows the emotional state, as reflected in changes in the sympathetic nervous system. Skin conductance changes (number and amplitude of the waves, as well as mean skin conductance level) were measured in connection with heel prick from 29 weeks gestational age. The purposes of this study were to examine the development of emotional sweating in preterm infants, and to correlate the changes in emotional sweating with the changes in behavioural state. Fifty infants' behavioural state and skin conductance changes were measured for 2 min before, 2 min during, and 2 min after heel prick. Half of the infants were between 29 and 31 weeks gestational age. They were divided into three sub-groups; 0-10, 11-20 and 21-30 days postnatal age. The other half of the infants were between 32 and 34 weeks gestational age and they were divided into three similar sub-groups. They changed their behavioural state 114 times. Infants from 29 weeks gestational age and more than 10 days old showed emotional sweating as measured by the number and amplitude of the waves that were lowest in sleep and highest during crying (p<0.05). The mean skin conductance level mirrored the behavioural state from 34 weeks gestational age (p<0.05).To conclude, skin conductance changes increased with the level of behavioural state from 29 weeks gestational age and more than 10 days postnatal age.