The subject of secondary methemoglobinemia has been briefly reviewed, and reference made to some of its causes that have been cited in the past Three patients are described in a family of 6 who were exposed to NaNO2 by the ingestion of fish illegally adulterated in an attempt at preservation. The patients'' course, their therapy with methylene blue, and available laboratory data have been recorded for the possible use of clinicians and investigators reviewing this subject in the future. In general, the patients affected were children; and the severity of the syndrome was most marked in the youngest. Clinically, they experienced nausea, vomiting, abdominal cramps, hypotension, loss of consciousness, and cyanosis within approximately thirty minutes after the ingestion of the NaNO2. There was one death. The lethal dose of sodium nitrite to the youngest, 14 kg patient was of the magnitude of 460 mg total, or 32.9 mgAg by approximation of his ingested portion of the fish.