Abstract Blowfly proboscis extension during stimulation of labellar sugar receptors can be inhibited by the presence of salt. The possibility that the salt receptor might initiate a central nervous inhibitory state is investigated behaviourally and electrophysiologically using simultaneous recordings from labellar chemoreceptors and the extensor muscle of the haustellum. While a mixture of 100 mM sucrose and 4 M NaCl applied to a single sensillum does cause inhibition, the same compounds applied separately simultaneously on separate sensilla do not. A mixture of 100 mM sucrose and 4 M NaCl does not produce central nervous effects such as motor response decrement to repeated stimulation; nor does it produce an enhanced motor response resulting from cross-channel summation when applied simultaneously with 100 mM sucrose on another sensillum. These results argue that the inhibitory effect of mixtures containing sugar and salt can be explained by inhibition of the sugar receptor without having to invoke a central inhibitory mechanism.