Melatonin maintains water consumption at baseline levels. Independent of rearing conditions the amount of liquid consumption containing vehicle for daytime (A) and nighttime (B) drinking during stage 2 (S2) increased significantly in relation to daytime and nighttime drinking for stage 1 (S1; Daytime: Veh-S1 versus Veh-S2, t = 3.07, P < 0.02 and Nighttime: Veh-S1 versus Veh-S2, t = 3.54, P < 0.005). Melatonin during stage 2 for both daytime (A) and nighttime (B) maintained the amount of drinking at baseline levels (stage 1; Daytime: Veh-Stage 1 versus Mel-S2, t = 0.08, P > 0.9 and Nighttime; Veh-S1 versus Mel-S2, t = 0.18, P > 0.85). *P < 0.05, Student t-test. Error bars represent s.e.m. Abbreviations: veh, vehicle; S, stage; Mel, melatonin.