Data on the structure, synthesis, stability and reactivity of sulfur-containing reducing agents with C–S or S–S bonds — sodium dithionite, sodium hydroxymethanesulfinate and thiourea oxides — are surveyed. Reactions of anaerobic and aerobic decomposition of sulfur-containing reducing agents are discussed. The applications of these compounds in the studies of non-linear phenomena in chemical kinetics and in guanidine syntheses are considered. The bibliography includes 165 references.