High-resolution deuterium NMR spectroscopy has been used to follow the detoxifying metabolism of [D2]formaldehyde in vivo in several bacterial species. Production of [D2]methanol in Escherichia coli confirms that the oxidation and reduction pathways of metabolism are independent in this organism. Efficient production of equimolar quantities of [D]formate and [D3]methanol in Pseudomonas putida F61a and Staphylococcus aureus implicates a formaldehyde dismutase, or "cannizzarase", activity. These observations imply that the unusual formaldehyde resistance in P. putida F61a is a direct result of efficient dismutation acting as a route for detoxification. Cross-dismutation experiments yield an enzymic kinetic isotope effect of ca. 4 for H vs D transfer and a similar spectrum of substrate specificity to the isolated enzyme. [D]benzyl alcohol produced by cross-dismutation of [D2]formaldehyde and benzaldehyde in P. putida is demonstrated to have the R configuration by a novel deuterium NMR assay. Additionally, S. aureus produces methyl formate as a product of formaldehyde detoxification, apparently by oxidizing the methanol hemiacetal of formaldehyde.