A group of 193 children, classified as high or low reactive to stimulation at 4 months and observed again at 14 and 21 months, were observed at 4 1/2 years of age for behavioral signs of inhibited or uninhibited behavior. Children who had been high reactive were less spontaneous and less sociable than those who had been classified as low reactive, but only a small proportion of children maintained a consistently inhibited or uninhibited phenotype at all ages.