The dietary intake of anticholinesterase (anti-ChE) agents was estimated in 331 schoolteachers during the spraying season. Summer plasma-cholinesterase (ChE) activity was compared with the baseline value obtained during winter. Intraindividual plasma-ChE activity varied independently of factors such as drugs, non-malignant diseases, alcohol and smoking. A depressed mean plasma-ChE, indicating an intake of anti-ChE agents (P = 0.04), was observed in individuals who consumed exclusively agriculturally-grown fruits and vegetables without an additional intake of unsprayed, home-grown products. It remains to be determined whether a subclinical but chronic intake of anti-ChE agents in the diet can be hazardous to humans.