The influence of factors such as type of pesticides used, use of personal protective devices and hygienic behaviour on acetylcholinesterase inhibition and activity levels in red blood cells of agricultural workers was studied in four areas in Kenya. Empirical modelling techniques were used to identify and quantify factors affecting acetylcholinesterase inhibition and activity. Use of personal protective devices was almost non-existent in areas 3 and 4 where mainly subsistence farmers were studied. Differences in hygienic behaviour between areas were relative small. WHO Class I pesticides were mostly found in area 1 (mainly large farms growing flowers) which also had highest amounts of pesticide use and highest frequency of pesticide spraying. Despite widespread use of protective devices in this area significant inhibition occurred. It became unclear whether acetylcholinesterase inhibition occurred as a result of protective clothing soaked with pesticides, thereby increasing dermal exposure, or because of other (unmeasured) factors. Inhibition, however, could have been much worse without protective devices. In area 1, most workers wore boots, which were found to be protective only when combined with an overall; wearing boots alone led to increased inhibition. Access to a washing facility or bathing facility had a positive effect on acetylcholinesterase levels. However, washing of hands and bathing immediately after spraying seemed reactive behaviour rather than proactive behaviour. Spraying was found to lead to more profound acetylcholinesterase inhibition than mixing. Workers who sprayed WHO Class III pesticides had less acetylcholinesterase inhibition than workers spraying more toxic pesticides.