The present invention relates to novel alternative forms of human acetylcholinesterase (AChE) and nucleotide sequences encoding the same. The genes encoding the novel forms of human AChE have been identified in various malignant tumor cells. In a further aspect, the invention relates to a transgenic animal assay system for evaluating efficacy of drugs against cholinergic proteins, prior to or in the course of therapeutic treatment. Transgenic animals, preferably developing tadpole of Xenopus or mice which express human AChE, are used. The transgenic animal assay system is also useful for evaluating the toxicity of substances which potentially block human AChE (e.g. organophosphorous compounds).