D-amino acid dehydrogenase was found to be solubilised from envelope preparations of Escherichia coli by treatment with detergents but not with aqueous buffer solutions. Triton X-100-solubilised dehydrogenase was found to rebind to envelope preparations from the wild strain (AB 259) and its D-amino acid dehydrogenase-less mutant (DAD 13), and activities higher than those of native envelopes could be obtained. Re-binding was stimulated by magnesium. D-alanine stimulated cytochrome reduction and oxygen uptake were reconstituted when the solubilised dehydrogenase rebound to AB 259 envelopes. Re-binding of solubilised dehydrogenase to DAD 13 envelopes was independent of the growth medium used for DAD 13.