By use of 2-(alkylthio) acetoacetic esters, for which an improved synthesis is described, a series of 4-alkylthio-2-pyrazolin-5-ones has been prepared and these have been converted into their methyl- and dimethyl-carbamic esters. In an alternative approach to these esters, methylthio-groups were introduced directly into the 4-position of certain 4-unsubstituted pyrazol-5-yl carbamates by reaction with methanesulphenyl chloride. Oxidation of the 4-alkylthiopyrazol-5-yl carbamates gave good yields of the corresponding sulphoxides and sulphones.