The overall crystal quality as well as the harvest period of bovine adenosine deaminase containing a zinc ion at the active centre has been compared in three different environments: crystallization as a control, crystallization with agarose gel and crystallization in a high magnetic field. In crystallization with agarose gel, the probability of obtaining high-quality crystals was somewhat increased, but the harvest period was elongated. On the other hand, in crystallization in a magnetic field, the probability of obtaining high-quality crystals was greatly increased. Furthermore, the harvest period for crystal growth in a magnetic field was much shorter than that with agarose gel.