Incorporating certain functional groups or atoms into surfactant molecules can have a dramatic impact on the surface activity of the chemicals. This paper summarizes how the introduction of sulfur atom into polyalkylene oxide frother molecules increased metal recovery, both copper and molybdenum, in the flotation of porphyrry ores. Both hydrophile-lipophile balance (HLB) numbers and collector/frother/mineral interactions are considered to play a role in enhancing recovery. (C) 2000 Elsevier Science B.V. All rights reserved.