A method for the direct determination of carbamate pesticides and their formulation by gas chromatography (GC) was developed. Four causes for the thermal decomposition of carbamates during GC were found, these being tarry matter remaining in the injection port, the active site on the glass column wall, neutral or weakly alkalic column packings, and inert ingredients of the formulation. To prevent carbamate decomposition by these causes, a dimethyldichlorosilane (DMCS)-treated glass insert injection port was used, which was always cleaned to remove any tarry matter, together with a DMCS-treated glass column, weakly acidic column packing (Thermon® 3000 on Shimalite® WP), and formic acid with which the formulation samples were injected into the GC. With these improvements, all of 8 N-methylcarbamates, i.e., BPMC, MPMC, MTMC, propoxur, aminocarb, bendiocarb, carbofuran and NAC (carbaryl), were de-termined directly and quantitatively with a 0.2% to 0.4% of coefficient of variation (C.V.). The formulations of BPMC, MPMC, MTMC and NAC were also directly determined with 0.3% to 0.6%C.V.