Physical and emotional stresses are known to increase the production and secretion of glucocorticoids by the adrenal cortex in both humans and experimental animals. The urinary corticoid: creatinine (C:C) ratio is increasingly used as a measure of adrenocortical function. In this study we investigated whether a visit to a veterinary practice for vaccination, a visit to a referral clinic for orthopedic examination, or hospitalization in a referral clinic for 1.5 days resulted in increases of the urinary C:C ratio in pet dogs. In experiment 1, owners collected voided urine samples from 19 healthy pet dogs at specified times before and after taking the dogs to a veterinary practice for yearly vaccination. In experiment 2, 12 pet dogs were evaluated in a similar way before and after an orthopedic examination at a referral clinic. In experiment 3, 9 healthy pet dogs were hospitalized for 1.5 days and urine samples were collected before, during, and after this stay. Basal urinary C:C ratios in all experiments ranged from 0.8 to 8.3 x 10(-6). In experiment 1, the urinary C:C ratio after the visit to the veterinary practice ranged from 0.9 to 22.0 x 10(-6). Six dogs had a significantly increased urinary C:C ratio (responders), but in 5 of these dogs the ratio was < or = 10 x 10(-6). In experiment 2, 8 of 12 dogs responded significantly with urinary C:C ratios ranging from 3.1 to 27.0 x 10(-6). In experiment 3, 8 of 9 dogs had significantly increased urinary C:C ratios, ranging from 2.4 to 24.0 x 10(-6), in some or all urine samples collected during hospitalization. In 4 dogs urinary C:C ratios 12 hours after hospitalization were still significantly higher than the initial values. Thus, a visit to a veterinary practice, an orthopedic examination in a referral clinic, and hospitalization can be considered stressful conditions for dogs. A large variation occurs in response, and in individual dogs the increases in urinary C:C ratios can exceed the cutoff level for the diagnosis of hyperadrenocorticism. Therefore, urine samples for measurement of the C:C ratio in the diagnosis of hyperadrenocorticism should be collected in the dog's home environment, to avoid the influence of stress on glucocorticoid secretion.