A new system for obtaining accurate and stable urine flow data was developed, in which patients have a key role in recording their own urinary flow data. Flow curves and urination data are recorded on an integrated circuit card, which the patient carries in a pocket. Before urinating, the patient inserts the card into the system. Urination data are recorded automatically. The card can record up to 14 days worth of urination data. A personal computer then calculates and prints all of the flow curves including maximum flow rate, average flow rate, voided volume, duration time, hesitation time, and date and time of urination. This system is useful for detecting subtle changes in urination patterns. Typical circadian rhythms for urination can also be recorded. With this integrated circuit card system the clinical course under alpha-blocker administration could be precisely monitored.