Dye-linked formaldehyde dehydrogenase (I) was partially purified (11-fold) from MeOH- and EtOH-grown Hyphomicrobium X. Through not homogeneous, it did not contain MeOH dehydrogenase, formate dehydrogenase, or cytochrome c. Methylphenazonium methylsulfate (II), cytochrome c, Wurster's Blue, dichlorophenolindophenol (III), and methylphenazonium ethosulfate could act as primary electron acceptors with apparent Km values for the first 3 substances of 0.69, 128, and 3.07 mM, resp. The activity of partially purified I could be maintained over 3 mo at -20 Deg in the presence of EtOH (10%). The mol. wt. of I was 83,500 and it was active from pH 6.5 to 9.0 with max. activity at pH 7.2 using cytochrome c as electron acceptor and at pH 7.6 when II and III were used. The Km values for formaldehyde, acetaldehyde, propionaldehyde, and heptaldehyde as substrates were 2860, 270, 13, and 2.5 mM, resp. I is probably a general aldehyde dehydrogenase not directly involved in the dissimilation of C-1 compds. [on SciFinder (R)]