We examined the stability of twelve control materials from different suppliers containing creatine kinase. The stability was assessed storing preparations at 4 °C, 27 °C and 37 °C and periodically measuring creatine kinase catalytic concentration. The activity was significantly greater when the lyophilized material was reconstituted with water at 4 °C as compared to 27 °C and 37 °C. All preparations tested showed good stability at 4 °C over a 72 hour period. We considered the suitability of tested control materials for quality-control purposes. © 1995, Walter de Gruyter. All rights reserved.