,2,3-trichloropropane (TCP) is a highly toxic and recalcitrant compound. Haloalkane dehalogenases are bacterial enzymes catalysing the cleavage of a carbon-halogen bond in a wide range of organic halogenated compounds. Haloalkane dehalogenase LinB from Sphingobium japonicum UT26 has, for a long time, been considered inactive with TCP since the reaction can not be easily detected by conventional analytical methods. Here we demonstrate detection of the weak activity (kcat = 0.005 s-1) of LinB with TCP using X-ray crystallography and microcalorimetry. This observation makes LinB a useful starting material for development of new biocatalyst towards TCP by protein engineering. Microcalorimetry is proposed to be a universal method for detection of weak enzymatic activities. Detection of these activities is becoming increasingly important for engineering of novel biocatalysts using the scaffolds of proteins with promiscuous activities.