Blood specimens from primary care centres are normally transported to central laboratories by mail. This necessitates centrifugation and separation, especially since the potassium ion concentration in whole blood changes during storage at ambient temperature. Thus, because of the growing awareness of and concern for pre-analytical contributions to the uncertainty of measurements, we investigated 27 components and their stability under controlled temperature conditions from 17 to 23 degrees C. We found that storage of whole blood can be prolonged by up to 8-12 h for all components examined, including potassium ions, when stored at 20+/-0.2 degrees C. We conclude that this opens the possibility for establishing a pick-up service, by which whole blood specimens stored at 20-21 degrees C can be collected at the doctor's office, making centrifugation, separation and mailing superfluous. In addition, the turn-around time from sample drawing to reporting the analytical result would be shortened. After investments in thermostatted boxes and logistics, the system could reduce costs for transporting blood samples from general practice centres to central laboratories.