Infant-care behavior patterns of captive cotton-top tamarins were examined to assess factors defining participation by non-reproductive helpers. The time spent carrying infants and characteristics of infant transfers were examined for 47 helpers in a total of 18 groups. We predicted that age, previous experience, and carrying opportunity would all affect participation of non-reproductive helpers. Our results confirm that carrying by non-reproductive helpers was related to age, with older helpers carrying more often. However, this difference declined with increasing infant age, suggesting that body size of the carrier was not the only factor determining participation in carrying. When observations were classified relative to type of interaction with infants, older juveniles were found to both investigate and harass infants more often than subadults or younger juveniles. There was no effect of gender on carrying. The carrying behavior of subadults was not affected by their previous experience; that is, subadults with no previous exposure to infants carried as often as those with previous experience. Inter-individual variation among helpers was high; within 11 twin litters of helpers, one animal usually carried significantly more than the other.