Lives and works with his wife Linda Johnston in California. He originally worked as a primary school teacher in the Netherlands from 1970 to 1978. He then began to train as a homeopath in the Hague, opening his own practice in 1979. At the same time, he translated several works of homeopathy. His first book appeared in 1985: “Kindertypes in Homoeopathie (Children's Types in Homoeopathy).” In 1990 he was appointed head of the school of homeopathy in Holland; soon afterwards, he started to give seminars around the world. Vermeulen has the rare ability to convey the essence of a remedy in a few well-chosen words. This ability is especially evident in his two works “Synoptic Materia Medica” volumes I and II. In his newest works, he deals particularly with nosodes. So far, two volumes have appeared, one on bacteria and viruses, and one on fungi.