Background: Previous experiments show that amphibian larvae are responsive to homeopathically prepared thyroxine.Methods: We studied the effect of a highly diluted and agitated thyroxine solution exposed to various electromagnetic fields on metamorphosis in highland Rana temporaria. The devices tested were: microwave oven, mobile phone, airport X-ray, and a red light barcode scanner. Animals were treated either with homeopathically prepared thyroxine (10−30 parts by weight, 10−35 in the water in which the animals were kept), or analogously prepared blank solution, or analogously prepared thyroxine exposed to the electromagnetic field of one of the devices tested. Solutions were administered at 48 h intervals according to a standardized protocol.Results: Animals treated with the standard test solution thyroxine 10−30 metamorphosed more slowly than the control animals, ie the effect of the homeopathically prepared thyroxine was opposed to the usual physiological effect of molecular thyroxine. The cumulative number of test animals that had reached the four-legged stage at defined points in time was smaller in the group treated with homeopathically prepared thyroxine at most of the points in time. This was found independently by all three research teams involved. In contrast, this effect did not occur when the thyroxine solution had been exposed to the field of the early model microwave oven, or mobile phone. There was no difference between aqueous or alcoholic solutions were used, and there was, if any, only a small protective effect from aluminum foil. Airport X-ray and red light barcode scanning did not diminish the effect of the homeopathic solution.