In order to develop a simple and sensitive method for detecting human polyomavirus DNA in the urine of patients by the polymerase chain reaction (PCR), it was found that the viral DNA could be released from urine by proteinase K and then amplified by PCR directly, without additional treatment such as ultracentrifugation or DNA extraction. Direct PCR amplification of viral DNA from urine was volume limited and 5 microliters of urine appeared to be the optimum amount for direct PCR amplification. When the urine volume was greater than 10 microliters, the results of PCR were inconsistent. However, the urine volume could be increased after dialysis to remove possible inhibitor(s) which may interfere with PCR. Direct PCR amplification of patient urine is convenient and eliminates several steps which can cause loss of DNA from the sample.