A comparison of blastogenic responsiveness to antigens and mitogen by human lymphocytes was made between cells which had been processed for culture immediately following blood collection and cells obtained from blood collected 9-11 hr previously and transported via commercial airline from the patients' homes to our laboratory. There were no significant differences in the responses of transported and non-transported cells if the blood was maintained at ambient temperature during the period of shipment. Chilling the blood during transport, however, resulted both in decreased stimulation of the cells and increased 'background' activity in unstimulated cultures. These findings indicate the feasibility of carrying out both limited immunological evaluations and extended periods of follow-up for patients located at considerable distances from a research laboratory.