To reduce renal cyst size in autosomal dominant polycystic kidney disease (ADPKD), minocycline hydrochloride solution was instilled into the enlarged cysts in three ADPKD patients. In one patient with reduced renal function, such sclerotherapy apparently diminished cyst size, but without apparent improving effect on renal function at 7 months of follow-up. The second patient, who needed the replacement therapy on admission, had been free from hemodialysis over 4 months after the therapy. Persistent flank pain disappeared in both patients. In the third patient with normal renal function, sclerotherapy was done to get a better control of hypertension. Initially blood pressure decreased, but it returned up to the pre-therapy level irrespective of definite reduction of the enlarged cysts at 8 months of follow-up. The therapy with minocycline hydrochloride did not appear harmful, and may be helpful in the management of ADPKD.