The germination of seeds of Arabidopsis thaliana, Lactuca sativa and Zinnia elegans were decreased by a 8-21 day-incubation in 90% relative humidity at 37 degrees C. An extremely low frequency magnetic field (ELFMF; 60 Hz, 5 mT) applied to the seeds during the incubation suppressed these decreases in the germination. The ELFMF suppressed irreversible deterioration of the seeds, rather than dormancy, probably preventing water absorption. ELFMF can be helpful for the storage of humidity-vulnerable seeds.