Sixteen patients acutely poisoned with aldrin were examined to evaluate a possible correlation between serum aldrin and dieldrin levels and clinical complaints. The patients were classified as having mild (N = 8), moderate (N = 5) or severe (N = 3) poisoning according to clinical symptoms. Concentrations of less than 20 micrograms/l were usually associated with mild poisoning, which involved complaints such as nausea, vomiting and epigastric pain, whereas concentrations of 100 to 200 micrograms/l were considered to represent moderate intoxication and were associated with nausea, vomiting, epigastric pain, headache, dizziness, and convulsions. Severe or fatal cases were associated with levels above 700 micrograms/l. Taken together, these results suggest that serum aldrin and dieldrin levels can be used as indicators of clinical prognosis after acute poisoning with these insecticides and that convulsions could suddenly occur even in the absence of prodromal signs or symptoms.