Reinhardt, V., Houser, W. D., Cowley, D. et al. 1989. Alternatives to single caging of rhesus monkeys (Macaca mulatta) used in research. Zeitschrift für Versuchstierkunde [Journal of Experimental Animal Science] 32, 275-279.

Single-housed rhesus macaques were transferred to permanent pair-housing arrangements. The present investigation also demonstrates that pairing caged rhesus monkeys with compatible conspecifics does not interfere with a number of common research protocols [e.g., headcap implantation, experimental surgery, blood collection]. Our experiences even suggest that distress related to handling or restraint is reduced by the presence of the familiar companion. [This work has also been published in: Humane Innovations and Alternatives in Animal Experimentation 3: 123-125, 1989; Reinhardt V; Alternatives to single caging of rhesus monkeys. ] http://www.awionline.org/lab_animals/biblio/h123.htm