In each of three trials, 150 day-old broiler chicks were eyedrop inoculated with 0.04 ml of high-passage F strain Mycoplasma gallisepticum (MG) and housed in biological isolation units at 10 chicks per unit. At 4 wk of age, 50 chickens were designated as controls and remained on tap water (pH 7.30), 50 chickens were provided tap water containing 0.63% ammonium chloride (NH4Cl, pH 6.91), and 50 chickens were provided tap water containing 1.26% sodium bicarbonate (NaHCO3, pH 8.17). Fluids were supplied for ad libitum consumption. At 5 wk of age, all chickens were swabbed from the choanal cleft for MG isolation and bled from the left cutanea ulnea vein for pH determination. As a percent of total swabs obtained, significantly fewer chickens that consumed water containing NH4Cl (38.3%) were positive for MG by culture compared with either the NaHCO3 group (61.3%) or the control group (67.6%). Nonmycoplasmal swab contamination was significantly higher for chickens that consumed water containing NH4Cl (59.7%) compared with either controls (31.8%) or NaHCO3-treated chickens (38.7%). When contaminated cultures were discarded, MG isolations from the tap water group were not significantly different from MG isolations from either the NH4Cl or NaHCO3 group. However, MG isolations from the NH4Cl group (95%) were significantly less compared with the NaHCO3 group (100%). Mortality was significantly higher in chickens that consumed water containing NaHCO3 (8.7%) compared with either controls (1.3%) or the NH4Cl-treated chickens (0.7%). Blood pH values were lower for the NH4Cl group (7.927), higher for the NaHCO3 group (8.093), and intermediate for controls (8.035). Results of this study suggest that water containing NH4Cl hinders the bacteriological recovery of MG from the choanal cleft.