The kinetics of oxidation of formaldehyde, formic acid and their deuterated isomers have been studied with chromic acid (part A) and also with vanadium (v), and cobalt (III) as oxidants (part B). In each case the reaction mechanism resembles that for the oxidation of a secondary alcohol by the same oxidant. Thus formaldehyde is oxidized in its hydrated form, H
2
C(OH)
2
. The quantitative study of kinetic and solvent effects leads to clarification of further details concerning secondary stages in the oxidations effected by chromic acid, whilst the determination of thermodynamic parameters for the oxidations by one electron abstracting reagents (part B) shows that any direct correlation between activation energies and kinetic isotope effects involves unwarrantable assumptions. It is probable that these reactions proceed through cyclic intermediate complexes.