Calorimetric investigations were made of the interactions of dimethylmercury (DMM) with various organic solvents and compounds in solution. Heats of solution of DMM in inert solvents cyclohexane and carbon tetrachloride and in active solvents benzene, pyridine, and p-dioxane were measured. The effects of nitrobenzene, thiophenol, and thiourea were also investigated. All heats of solution were endothermic and less than 0.6 kcal/mole. No indications of specific interactions were observed for any of these compounds. The apparent solubility of DMM in water and in aqueous electrolyte solutions was determined using flameless atomic absorption spectrophotometry. The term apparent solubility is used to specify the total concentration of all forms of mercury in an aqueous phase in prolonged contact with an excess of DMM. The presence of halide ions was found to greatly increase the apparent solubility of DMM, with more than a tenfold increase in 1 M NaCl. (Author Modified Abstract)