Abstract The respiratory response to acute inhalation of hydrogen sulfide (H 2S) and the response of intrapulmonary CO 2 receptors to this gas were studied in male White Leghorn chickens. Inhaling low concentrations of H 2S (0.05%) for 30 min had no effect on ventilation, but respiratory frequency and tidal volume became irregular and variable in birds that inhaled 0.2% and 0.3% H 2S for that period. All birds that inhaled 0.4% H 2S died within 15 min. H 2S, presented in the gas stream omnidirectionally ventilated birds, caused an increase in the discharge frequency of intrapulmonary CO 2 receptors and an increase in the amplitude of sternal movements. Because an increase in the discharge of these receptors normally inhibits the central respiratory neurons and may lead to apnea, it is clear that H 2S also has actions that increase the output from these central neurons. The possibility that H 2S affects the intrapulmonary CO 2 receptors by inhibiting carbonic anhydrase in them is discussed.