The purpose of the present research was to clarify whether or not the stress of preterm infants can be relieved by "wrapping up" during measurement of their body weight. The body weights of four preterm infants were measured using alternately our facility's traditional method, whereby babies are taken naked as they are from the incubator ("traditional method"). and a method whereby the infants were taken out clothed in a towel so that their bodies except for the head were covered in fabric ("wrap-up method"). Each infant's body weight was measured 3 times using the two methods, making a total of 12 cases. Before weight measurement the infants were put into a restful state; subsequently they were examined for behavioral aspects (stress signs and state) during (a) weight measurement. (b) the 5 minute period immediately after weight measurement (minutes 0 to 5). and (c) the subsequent 5 minute period (minutes 6 to 10). Below are the results of the comparison that was made of the behavioral aspects in each of these periods. A significant difference occurred in stress signs during weight measurement, with just 7 out of 14 signs being observed with the wrap-up method. During the 1st (minutes 0-5) and 2nd (minutes 6-10) 5 minute periods following weight measurement the number of stress signs observed was small compared to those occurring during weight measurement, but again there was a significant difference. As regards stress state, the result obtained was that no increase whatever was observed during weight measurement when the wrap-up method was used. These results indicate that the wrap-up method is useful for relieving stress in premature babies during body weight measurement. In the future it will be necessary to read accurately the stress signs in babies under all types of care and to explore methods to remedy such stress.