Social housing remains one of the best forms of environmental enhancement for nonhuman primates (NHPs). The gradual steps (GS) method, a 2-step plan involving an initial phase of limited physical contact (protected contact [PC]) prior to full contact (FC), is widely used for introducing macaque pairs. Recent evidence has suggested that administration of diazepam prior to FC introduction, without a PC phase, improves the success rate of pairings among adult male rhesus macaques (Macaca mulatta). Nevertheless, given the popularity of the standard GS method, there is considerable interest in using diazepam along with this technique. We hypothesized that administering a single dose of diazepam prior to the PC phase would improve the success rates of isosexual pairings of unfamiliar adult macaques. Twelve males and 12 females were studied in each of 3 groups, with 2 different doses of oral diazepam (2.5 or 3.2 mg/kg) and controls introduced without diazepam. Pairs were deemed successful after 14 consecutive days of compatible FC housing. Among males, success rates for the low diazepam, high diazepam, and control groups were 67%, 50%, and 67%, respectively. Among females, the corresponding values were 50%, 33%, and 17%. There were no significant differences in overall introduction success rates for either sex. However, among females, the success rates during the initial PC phase were significantly higher in introductions involving the lower dose of diazepam (83%) than among controls (33%). Descriptively, in both sexes, less severe wounding patterns were observed with the lower dose compared with either the high dose or control groups. Our results suggest that diazepam administration prior to the PC phase of the GS method does not improve pairing outcomes for either sex in rhesus macaques. However, diazepam may have some utility in moderating wounding during unsuccessful introductions.