The influence of different amounts of oral sodium intake combined with high oral water intake on potassium excretion and plasma potassium concentration (PK) was evaluated. Female beagle dogs (11-16 kg) were divided into 2 groups: 1. Normal Sodium and high Water Intake (NSWI): 2.5 mmol Na, 3.55 mmol K, 91 ml H2O, and 277 kJ per kg body mass and 24 h (31 24 h-balance studies with 11 dogs). 2. High Sodium and high Water Intake (HSWI): Same diet as NSWI but 14.5 mmol Na x kg body mass-1 x 24 h-1 (55 24 h-balance studies with 21 dogs). The 24 h-balance studies were performed after different periods of time after onset of the respective diet (dogs in metabolic cages). Plasma sodium concentration (PNa) on NSWI was 148.4 +/- 2.6 mmol x 1(-1), whereas it was lower on HSWI (145.9 +/- 2.4 mmol x 1(-1). The lower plasma aldosterone concentration (PAC) on HSWI (24 +/- 8 pg x ml-1) compared to NSWI (67 +/- 38 pg x ml-1) may account for the lower PNa on HSWI. 24 h-sodium excretion was 93.6 +/- 6.5% of intake (%i) on HSWI and 91.5 +/- 20.7% i on NSWI. 24 h-water excretion was not different between both groups (81 +/- 7% i). PK was 3.93 +/- 0.25 mmol x 1(-1) on NSWI regardless of the time the dogs were on NSWI.(ABSTRACT TRUNCATED AT 250 WORDS)