Reinhardt, V., Cowley, D., Scheffler, J. et al. 1990. Cortisol response of female rhesus monkeys to venipuncture in homecage versus venipuncture in restraint apparatus. Journal of Medical Primatology 19, 601-606.

All subjects were well habituated to blood collection, and it was not necessary to immobilize them; they readily presented a leg for venipuncture. In single monkeys venipunctured in the restraint apparatus, cortisol concentrations were on average 50% higher 15 minutes after venipuncture; this elevation was significant (p<0.001). The magnitude of cortisol elevation was only 18% in single monkeys venipunctured in the homecage; this elevation was not significant (p>0.1).Single, dominant-paired and subordinate-paired monkeys had equivalent cortisol concentrations. It was concluded that living with a compatible companion does not constitute a situation that is more distressing than living alone.