A series of halophenols was prepared by the reaction of bis(hydroxyphenyl)methanes with effective halogenating agents such as bromine and sulfuryl chloride. One of these compounds, a biologically active halophenol--2,2',3,3'-tetrabromo-4,4',5,5'-tetrahydroxydiphenylmethane (1)--frequently isolated from red algae, was synthesized for the first time. Other halophenols included several novel compounds, together with known derivatives that were synthesized from the phenolic intermediates, bis(3,4-dihydroxyphenyl)methane (5) and bis(2-hydroxyphenyl)methane (14). All of the synthesized compounds were tested for antimicrobial activity against Gram-positive, Gram-negative bacteria and fungi. The preliminary structure-activity relationship was investigated in order to determine the essential structural requirements for their antimicrobial activity. Of all these halophenols, 2,2',3,3',6-pentabromo-4,4',5,5'-tetrahydroxydiphenylmethane (8) was found to be the most active against Candidaalbicans, Aspergillusfumigatus, Trichophytonrubrum, and Trichophytonmentagrophytes while 3,3',5,5'-tetrachloro-2,2'-dihydroxydiphenylmethane (18) exerted a powerful antibacterial effect against Staphylococcusaureus, Bacillussubtilis, Micrococcusluteus, Proteusvulgaris, and Salmonellatyphimurium.