On the basis of an investigation og 193 healthy adults without occupational exposure to known cholinesterase-inhibitors, it was found that in addition to being related to the sex and ChE-fenotype, the cholinesterase activity is correlated to the weight and height of the individual concerned. Compared with the great interindividual variations, the intraindividual variations are of marginal significance for the total variation. Where dissimilar groups are concerned, comparison of the cholinesterase values corrected for variations which may be ascribed to the factors: sex, ChE-fenotype, weight and height is recommended.