uWe investigated the use and function of coda communication by sperm whales (Physeter macrocephalus L., 1758 (= Physeter catodon L., 1758)). Codas are stereotyped patterns of clicks often made by sperm whales in social contexts. We used the pulsed structure of coda clicks recorded from socializing female/immature groups to estimate the bodylength distribution of the animals producing the codas. Ninety-five percent of the 10653 codas that we measured were produced by whales measuring from 9 to I I m. This size range corresponds to the lengths of mature females. We compared these data to a length distribution calculated from photographic measurements of individuals from the same groups encountered during the same studies. There were more whales shorter than 8.5 m (10.0%) and longer than 12.5 m (2.7%) in the photographic length distribution than in that of the coda producers (0.30% and 0.08%, respectively). Since males leave their natal group when they are shorter than 9 m and return to breeding areas when they measure 13 m or more, our data show that the codas were produced almost entirely by mature females. We suggest that coda communication serves several functions, including social bonding.