The possible influence of the marine biogeochemical sulfur cycle on the global climate has been a topic of much recent research. Based on the hypothesis that phytoplankton could affect cloud albedo by producing dimethylsulfide, which is a precursor to aerosols and cloud condensation nuclei, and that cloud albedo could in turn affect the productivity of the phytoplankton, the presence of such a feedback cycle would have significant implications for models of global climate change. By considering available data on the relationships between individual components of the proposed feedback, an empirical model is developed of the cycle as a whole, allowing an assessment to be made of the degree to which the cycle could thermostatically regulate the climate. It is estimated that the feedback strength is about 20% (10%--50%) of that which would be necessary to completely counteract a perturbation to the global climate, such as is anticipated due to accumulation of anthropogenic greenhouse gases. ¿ American Geophysical Union 1993