The aim of this study was to determine residual urine and frequency of urination in normal male and female dogs and to compare these with dogs with neurogenic and obstructive dysuria. The bladder volume before urination was estimated ultrasonographically in 99 dogs (48 normal and 51 abnormal dogs). Each animal was then taken outdoors and walked on grass for 10 minutes. The number of attempts to urinate (successful or not) was recorded. Bladder urine volume after urination was then calculated. Normal females made only one or two (100 per cent successful) attempts to urinate while males a mean of 6.9 attempts (mean 75.4 per cent successful) within 10 minutes. The residual urine per kg body weight of normal dogs varied from 0.1 to 3.4 mi kg(-1) (median 0.2 mi kg(-1)). The residual urine volumes of normal dogs were significantly less (P<0.0001) than those of dogs with neurological disorders or obstructive disease. Ultrasonographic estimation of residual urine volumes could be valuable in diagnosing suspected neurological or obstructive bladder disease and in monitoring the response to treatment. (C) 1999 Harcourt Publishers Ltd.