1 This study was conducted with the aim of evaluating the impact on health produced by the use of different types of pesticides in greenhouses. It is based on the need to practice and develop biological monitoring techniques to assess exposure and predict health risk in workers occupationally exposed to pesticides. 2 Two groups of greenhouse workers with either high or low exposure to a combination of pesticides was taken in Almería, a Spanish province where cultures under plastic are very extended. 3 One hundred and five sprayers were interviewed to collect information about symptoms and signs related to past exposures. Each pesticide sprayer was examined by a physician, and a blood sample was drawn for plasma and red blood cell cholinesterases, complete blood count, and liver and renal function tests. 4 Exposure of workers to a combination of pesticides resulted in 37% of the workers showing toxic signs and symptoms. The main toxic effect observed were a high incidence of spontaneous abortion, depression, and certain neurologic disorders like headache, tremor and paraesthesia. 5 The major analytical change was a decrease of the mean corpuscular haemoglobin concentration in 38% of the cases. However, no significant decrease in both serum and erythrocyte cholinesterase activities was observed. 6 The sprayers were not usually aware of the potential hazards of pesticides and did not try their best to maintain personal hygiene.