The cholinesterase (ChE) activities were measured in-season and out-season in a total of 204 greenhouse workers and 360 non-exposed controls. No seasonal ChE variation were observed in the controls, whereas an in-season depression was seen in the workers, indicating an uptake of anti-cholinesterase agents during cultivation of greenhouse flowers in the intervals between sprayings (p = 0.0001). The anti-ChE agents applied seem to persist in the greenhouses and cause continued subtoxic uptake for weeks since last application. Wearing of protective gloves did not prevent the uptake. Thus, chronic percutaneous and oral uptake occurs as a result of cultivation of greenhouse flowers.