YACHIYODA SZ-5000 is a new model of lithotriptor made in Japan, of which the energy source is microexplosion. Compared with the old type of SZ-1, the water bag is substituted for a hot water bath and ultrasonography as well as fluoroscopy can be used for stone localization. Moreover, this new model is extremely small. The first clinical trial of 32 candidates with urinary tract calculi (34 stones) was performed at our hospital between September 1991 and June 1992. They were 10 women and 22 men between 25 and 71 with a mean of 47.3 years. All patients received no anesthesia. The stone location was: R2 for 16 stones, R3 for 5, U1 for 9, U2 for 1, and U3 for 3. The mean size was 14.1 mm. A mean number of 364, 326 and 324 shock waves were given for the R2, 3, U1, and U2, 3 stones, respectively. The second or third sessions were performed on 7 patients. Obvious symptoms and signs observed during the treatment were; local pain in 9 patients, nausea in 3, hypotension and bradycardia in 6, and hypertension in 3. Posttreatment fever up was found in two patients. In 34 stones, the efficiency evaluated 3 months later was 85.0% as determined by kidney-ureter-bladder X-ray and intravenous pyeography. In conclusion, YACHIYODA SZ-5000 is useful and safe in the management of patients with urinary tract stones.