All over the world, pesticides are frequently used in large quantities. Even though these substances are potentially toxic and may affect the human health, depending on the degree of exposure, contamination, and toxicity, they are nevertheless constantly released into the environment. Currently, predominantly organophosphorus (OP) and carbamate (CBM) pesticides, which are considered neurotoxic due to their potential to inhibit cholinesterase (ChE) activity, are used frequently in developing countries. Accordingly, many intoxication symptoms regarding these chemicals are diagnosed via the ChE analysis and its degree of inhibition. This is therefore the method of choice for biomonitoring exposed individuals, and has been described in the evaluation of thirteen Brazilian studies, which we retrieved from different online databases and present in this review. However, conflicting results on the effects on ChE as a result of repeated and prolonged exposure to low doses still prevail, mainly because farmers are usually exposed to mixtures of pesticides simultaneously.