ABSTRACT.The literature contains contrary reports with respect to the control of the proboscis extension of blowflies in response to stimulatory solutions. Control could be effected centrally, peripherally or by a combination of both. In this report a comparison of (i) behavioural responsiveness to sucrose (measured by tarsal thresholds for proboscis extension) and (ii) sensitivity of tarsal sugar receptors (measured from 0.1 to 1.1 s after stimulus onset) both before and 1 h after feeding of maleProtophormia terraenovaesuggests that the observed decrease in behavioural responsiveness after feeding is due to central inhibition rather than to a decline in peripheral sensitivity.