In this report, we evaluate the stability of urinary gonadotropin peptide (UGP), an urinary tumor marker for trophoblastic malignancies, which is also promising for other types of cancer. The concentrations were independent of the duration of storage (p > 0.1), but the mean difference between UGP values for samples stored at 4 degrees C and those kept at room temperature is 5.5% (p < 0.002), with the higher values for refrigerated samples. We conclude that UGP is stable at room temperature, allowing mailing of urine samples. Refrigerated (4 degrees C) samples show slightly increased values. However, this will have no clinical relevance in monitoring cancer patients.