Abstract There has been a substantial history of correlative associations between subtle changes in geomagnetic intensity and the prevalence of multiple sclerosis. Several experiments have shown that rats in which experimental allergic encephalomyelitis had been induced respond to naturally-patterned weak magnetic fields. Exposures of only 6 min once per hour during the scotophase to a ~ 50 nT, 7 Hz magnetic field whose amplitude modulations simulated a sudden geomagnetic storm commencement markedly reduced both the behavioural symptoms and mononuclear cell infiltrations. In the present study planarian were exposed for only 6 min per day for three days to this same field pattern and intensities but with or without the presence of the demyelinating agent cuprizone. Behavioural analysis indicated a strong interaction after one day of exposure between cuprizone and field conditions for the numbers of “head whips” and an indicator of “unusual behaviours.” The 6 min exposures to the patterned magnetic field on the second and third days eliminated the effects of cuprizone upon the numbers of head whips and related anomalous behaviours. General activity was not affected. The specificity of the simultaneous exposure to the magnetic field and cuprizone for normalizing the planaria is consistent with the results of rodent studies involving one model of multiple sclerosis and suggests that this paradigm might be useful for examining the potential mechanisms for the correlation between prevalence of MS and geomagnetic variables.