Plasma and erythrocyte cholinesterase levels were followed in 16 field workers exposed to organophosphate pesticides. The workers were part of a crew exposed to mevinphos (7786347) and phosphamidon (13171216) while tying leaves in a cauliflower field in Salinas Valley, California. Workers entered the field 6 hours after it was sprayed, despite state regulations requiring a 72 hour interval between pesticide application and reentry. Clinical signs occurred shortly after reentry. Symptoms of toxicity included blurred vision, eye irritation, dizziness, weakness, disorientation, headache, nausea, vomiting, and cramping. Two workers lost consciousness and were transported for emergency treatment. Workers received antidotal therapy based on individual decisions to see a physician. Seven persons received oral pralidoxime, one received intravenous pralidoxime and atropine, and two received atropine alone. Weekly blood samples were assessed for plasma and erythrocyte cholinesterase activity until symptoms abated. Plasma cholinesterase values were inhibited by about 66 percent in eight workers receiving medical attention within 24 hours. Erythrocyte cholinesterase values were decreased by approximately 33 percent in these individuals. Plasma and tissue cholinesterase activities showed respective reductions of about 34 and 39 percent 11 days after exposure. Regeneration to 95 percent normal activity averaged 57 and 66 days, respectively, for plasma and erythrocyte enzymes. No significant difference was determined for regeneration rates between individuals who received pralidoxime and those who did not. The authors note that problems are inherent in using postexposure cholinesterase values in the absence of baseline data to diagnose and follow cases of organophosphate poisoning. They conclude that symptoms of cholinesterase poisoning are better correlated with rapidity of cholinesterase decline than with absolute value of reduction in activity.