The functional communication systems of four physically disabled children with severe speech impairment were evaluated in terms of: (1) perceived dominant modes of communication; (2) observed frequency of communication mode occurrence; and (3) role of communication device in total communication system. All four subjects used a range of communication modes to reflect personal and listener preferences, and in response to differing conversational requirements. 'Standard' communication modes were mentioned more frequently by teachers and parents, and were observed more frequently in interactions. Augmentative and alternative communication devices played a limited but important role within total communication systems. A hierarchy of influences affecting the choice of communication mode is suggested.