This project investigates the effects of neurological and pharmacological interventions on the incidence and structure of squirrel monkey vocalizations emitted during volcalization-inducing contexts in a laboratory setting. This year, three separate studies were conducted. In one, the role in vocal production of the medial frontal cortex was studies following anterior limbic and neocortical ablations. Postoperative testing completed on four animals provide evidence for a concerted involvement of pregenual and preseptal limbic cortex together with an as yet undefined area of adjacent neocortex in the normal expression of the isolation call when the subject is visually and acoustically separated from conspecifics. The other two studies employed behavioral pharmacological techniques to examine the role of specific neurochemical substrates in mediating squirrel monkey vocal behavior. One of these studies investigated the role of drugs showing specific binding for alpha-adrenergic receptors. Clonidine in a dose of 0.1 mg/kg i.m. consistently decreased or eliminated isolation calls in subjects separated from conspecifics. Yohimbine in a dose of 0.2 mg/kg reversed the clonidine-related suppression of vocalization in this context, and, in addition, enhanced production of another vocalization, the twitter. In a second pharmacological study, benactyzine, an anticholinergic, was found to potentiate the induction of alarm calls given in response to a model predator. This same drug failed to significantly alter production of isolation calls.