Summary: Sera from 136 sub-human primates representing six genera were tested for the presence of antibody to Chikungunya, Semliki Forest Kumba strain, Onyong-nyong strain MP 87 and Mayaro strain B viruses. Twenty-six per cent of the sera tested were positive for N antibody to one or more of these agents. The extensive serologic overlap occurring between these viruses precluded any definitive interpretation of the results as to which virus may have been the specific infecting agent. Thirteen per cent of the sera tested were positive for CF and HI antibody to CHIK virus. In every instance a positive CF and HI response was associated with the presence of N antibody. Attempts at viral isolation from those sera of recent imports showing CF and HI antibody were unsuccessful. That extreme care should be exercised in the selection of lower primates for purposes of studying exotic viral agents is clearly indicated by the data presented. Although no viremia was found in the animals tested, adherence to a rigid program of housing and protective screening is essential if a serious transmission hazard is to be minimized, particularly in areas of high arthropod activity.