Esterases and lactate-(LDH) and malate-(MDH) dehydrogenases of 34 strains of Alcaligenes faecalis, 16 strains of A. denitrificans subsp xylosoxydans (A. xylosoxydans), 5 strains of A. piechaudii, and 10 strains of A. denitrificans subsp denitrificans (A. denitrificans) were analyzed by horizontal polyacrylamide-agarose gel electrophoresis. Four types of esterases were identified in A. faecalis, 3 in A. xylosoxydans, 3 in A. piechaudii, and 14 in A. denitrificans by their spectra of hydrolytic activity towards five synthetic substrates. Four variants of MDH and no LDH variant were detected in the strains of A. faecalis. MDH and LDH were distributed in three variants among the strains of A. xylosoxydans. Only one variant of MDH and two variants of LDH were found in A. piechaudii strains. Four variants of MDH and one variant of LDH were identified in the strains of A. denitrificans. A correspondence analysis of these results allowed precise identification of all the strains within these four species of Alcaligenes.