White bands resulting from precipitation of dodecan-1-ol liberated by hydrolysis of sodium dodecyl sulfate and decan-5-ol released by hydrolysis of decan-5-yl sulfate produced zymograms of the primary and secondary alkylsulfatases from Pseudomonas C(12)B. Gas-liquid chromatographic analyses of ether extracts of the precipitate-containing segments of the zymograms confirmed the identity of the alcohols which were not discerned in extracts of segments of the gels other than those containing precipitates. beta-Galactosidase from Escherichia coli was marked on zymograms by the liberation of o-nitrophenol from o-nitrophenyl-beta-D-galactoside, and arylsulfatase from Pseudomonas C(12)B was marked in gels by liberation of p-nitrophenol from p-nitrophenyl sulfate. Membrane-associated dissimilatory nitrate reductases from a nitrate respirer (Enterobacter aerogenes) and a denitrifier (Pseudomonas perfectomarinus) did not penetrate either 6.8 or 3% polyacrylamide gel but were demonstrable at the top of the gels. In the membrane-bound state, formate served as electron donor for nitrate reductase from E. aerogenes, and reduced nicotinamide adenine dinucleotide (NADH) served as donor for nitrate reductase from P. perfectomarinus. Both enzymes reduced nitrate at the expense of reduced benzyl viologen as well. Assimilatory nitrate reductase from E. aerogenes moved easily into the 6.8% gels (R(f) = 0.43 under the conditions of these experiments). The reduced dye served as electron donor for the assimilatory reductase, but formate and NADH did not. Incubation of the membrane-associated nitrate reductases with 2% Triton X-100 solubilized the enzymes and removed the capacity of formate and NADH to serve as electron donors. Both retained the ability to reduce nitrate at the expense of reduced benzyl viologen. The solubilized dissimilatory reductase from E. aerogenes moved further in the gels (R(f) = 0.49) than the soluble assimilatory reductase; the solubilized dissimilatory reductase from the denitrifier, P. perfectomarinus, moved further in the gels (R(f) = 0.64) than either of the enzymes from E. aerogenes.