Most Nyulnyulan languages (non-Pama-Nyungan, Western Australia), show an unusual clause type, the medio-active, with the case-frame of a transitive clause, but the verbal agreement of an intransitive clause; there is no formal registration in the verb. This paper provides a detailed description of the structural and semantic properties of this clause type in each language that exhibits it, identifying shared features and differences. Evidence is presented that it represents a distinct construction, of intermediate transitivity, and a grammatical analysis is proposed in terms of roles. The medio-active shows, however, few characteristics prototypical of the passive, and is not a voice option.