This investigation was carried out to determine the solubility of methanethiol in a methyldiethanolamine (MDEA) solution, Measurements were made in the absence of acid gases, H2S and CO2, with individual acid gases present, and with mixtures of acid gases present. Initially, measurements of the solubility of methanethiol in water were made at temperatures between 25 and 100 degrees C to confirm the sampling and analytical techniques. Experiments with an aqueous solution of 50 mass% methyldiethanolamine were carried out at 40 and 70 degrees C. The total pressure for most of the experiments was 6890 kPa, which was maintained by methane. Partial pressures of methanethiol ranged from 0.4 to 557 kPa.