Enzymatic synthesis of methyl halides through an S-adenosyl methionine transfer mechanism has been detected in cell extracts of Phellinus promaceus (a white rot fungus), Endocladia muricata (a marine red algae), and Mesembryanthemum crystallium (ice plant). This mechanism represents a novel pathway for the formation of halometabolites. The Michaelis constants for chloride and bromide ion and for S-adenosyl methionine in the reaction have been determined for the enzyme from E. muricata. A recent survey of marine algae indicates that there may be a broad distribution of this enzyme among marine algae.