A study investigated acquisition of three independent yet simulatneously produced morphological systems in American Sign Language (ASL): the linguistic use of space, use of classifiers, and inflections for aspect, all information incorporated into the production of a sign. Subjects were 30 deaf children with severe or profound prelingual hearing loss: four groups of native signers (ages 3, 5, 7, and 9) and two groups of late signers (ages 5 and 9, introduced to signing at age 2-4), each containing five children. Subjects looked through and then signed a story from a picture book. Their performance in using seven morphologically complex verbs was analyzed. Results showed striking differences between native and late signers on all measures relating to the internal complexity of the analyzed verbs, while measures unrelated to internal complexity did not show the same kind of qualitative differences. The pattern of development found indicates that the native signers use the morpheme as their basic linguistic unit of analysis, while late signers use the lexical item itself. This difference does not exist at the sentence level. The findings support claims that late signers treat signs as gestalts rather than as independent, simultaneously-produced systems and experience impaired later morphological development. (MSE)