A commercially available two-site solid phase radio-immunoassay was used to study the influence of time and temperature on the in vitro stability of CA 125. In whole blood samples stored at 20 degrees C the CA 125 immunoreactivity increased significantly after 2 days of storage. However, serum could be stored at 20 degrees C for 3 days and at -20 degrees C and -80 degrees C for three weeks without statistically significant changes in the CA 125 immunoreactivity. Therefore, for storage up to 3 days at 20 degrees C, serum should be preferred. For prolonged storage serum samples should be kept at -20 degrees C or -80 degrees C.