The red swamp crayfish Procambarus clarkii (Crustacea: Decapoda), one of the most invasive species of freshwater habitats, relies on chemical cues to locate food resources. Here we investigate the sensitivity spectra of the walking leg chemoreceptors to different compounds of possible feeding significance in relation to the omnivorous habits of P. clarkii. Extracellular nerve recordings showed that the disaccharides trehalose and cellobiose were the most stimulating sugars for leg chemoreceptors, but to a different extent: an extremely phasic time course for trehalose, more tonic for cellobiose. They were also comparable in stimulating effectiveness with the amino acids leucine and glycine (phasic-tonic responses), with different chemoreceptors being tuned to single compound classes. Leg chemoreceptors were also responsive to the monosaccharides glucose and fructose, taurocholic acid and, to a lesser extent, asparagine. Behavioural trials confirm the electrophysiological observations and assign an attractive role to all tested compounds. Such information may be helpful in the identification of key chemicals for crayfish, also aimed at the future development of strategies for population control programmes