Mutations of the Caenorhabditis elegans dystrophin/utrophin‐like dys‐1 gene lead to hyperactivity and hypercontraction of the animals. In addition dys‐1 mutants are hypersensitive to acetylcholine and acetylcholinesterase inhibitors. We investigated this phenotype further by assaying acetylcholinesterase activity. Total extracts from three different dys‐1 alleles showed significantly less acetylcholinesterase‐specific activity than wild‐type controls. In addition, double mutants carrying a mutation in the dys‐1 gene plus a mutation in either of the two major acetylcholinesterase genes (ace‐1 and ace‐2) display locomotor defects consistent with a strong reduction of acetylcholinesterases, whereas none of the single mutants does. Therefore, in C. elegans, disruption of the dystrophin/utrophin‐like dys‐1 gene affects acetylcholinesterase activity.