Yurakaré (unclassified, central Bolivia) marks core arguments on the verb by means of pronominal affixes. Subjects are suffixed, objects are prefixed. There are six types of head-marked objects in Yurakaré, each with its own morphosyntactic and semantic properties. Distributional patterns suggest that the six objects can be divided into two larger groups reminiscent of the typologically recognized direct vs. indirect object distinction. This paper looks at the interaction of this complex system of participant marking and verbal semantics. By investigating the participant-marking patterns of nine verb classes (four representing a gradual decrease of patienthood of the P participant, five a gradual decrease of agentivity of the A participant), I come to the conclusion that grammatical roles in Yurakaré can be defined semantically, and case frames are to a high degree determined by verbal semantics.