Hexamine, derived from solid fuel tablets, is a potential source for a number of home-made explosives including the primary high explosive hexamethylene triperoxide diamine (HMTD). Therefore, a means to characterise hexamine samples and to link HMTD with precursor hexamine may provide investigative intelligence to counter-terrorism agencies. We report the hydrogen, carbon and nitrogen isotopic compositions of hexamine isolated from retail samples of solid fuel tablets. Hydrogen isotopic compositions ranged from –123.0 to +172.6‰, carbon isotopic compositions from –47.1 to –27.6‰ and nitrogen isotopic compositions from –3.1 to +0.3‰. Despite within- and between-tablet inhomogeneity, a combination of these data could be considered characteristic of specific brands or manufacturers. Ten samples of hexamine were each used to synthesize four batches of HMTD using two isotopically distinct sources of hydrogen peroxide. The δ13C and δ15N compositions of the HMTD ranged from –48.8 to –31.5‰ for carbon and from +13.7 to +17.8‰ for nitrogen. δ2H compositions across all batches of HMTD was much wider than previously reported; –109.3 to +196.6‰. The changes in carbon and nitrogen isotopic compositions, progressing from hexamine to HMTD, could be explained by a reaction mechanism involving the decomposition of hexamine to methylimine and formaldehyde. Data also supported a mechanism whereby the hydrogen atoms of HMTD were derived from hexamine and not from other reagents. Based on the relationships Δ2HHEXAMINE-HMTD and Δ13CHEXAMINE-HMTD, a rule-of-thumb was proposed to identify possible hexamine precursors of HMTD.