Electroantennogram (EAG) and single-cell recording techniques have been used to demonstrate the presence of separate receptors for (-)-threo- and (-)-erythro-4-methyl-3-heptanol on the antenna ofS. scolytus. The majority of single-cell recordings showed spikes of two different amplitudes. The cell giving spikes of larger amplitude responded to the (-)-threo stereoisomer while the cell with the small-amplitude spikes responded to (-)-erythro-4-methyl-3-heptanol. It is suggested that in most recordings the two cells are associated with a single sensillum basiconicum.