Around 1970 LeSassier found a teacher of Chinese medicine and persuaded the man to allow him to apprentice with him. He learned about the energetics of medicinal herbs and developed an individualized diagnosis system. By the 1970s, he was one of the most well-known herbalists in the country. In 1983, he settled in New York City and opened Chiron’s Magic Minerals, where he practiced and taught herbs, bodywork, and energy work. William closed Chiron's in 1989 and moved his practice into the office of Dr. Steven Schram at 132 East 28th street. The back yard of the office was home to many herbs that William grew there including nettles, hops, raspberries, spilanthes, comfrey, holy basel and catnip.