The ultrastructure of pedipalpal and tarsal setae ofPhytoseiulus persimilis Athias-Henriot has been investigated by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The setae on top of the tarsi of the pedipalps are innervated by either 11–12 dendrites or 4–8 dendrites. Two of these dendrites terminate in tubular bodies, just below the articulation membrane of the sockets present at the setal base. Only one seta in the centre appears to be provided with two pairs of tubular bodies. Cross-sections of the palp tarsal setae revealed a crescent-shaped lumen and a rounded lumen, but just below the tip a small porous area is indicated by the exclusive presence of some blobs of material on the external hair shaft. These blobs are presumed to be secreted through terminal pores. The ultrastructure of the palpal setae is in agreement with the description of known contact chemoreceptors in insects, ticks and spiders. The sensilla on the dorsal surface of the anterior tarsi are either long, tapering socketed setae or short, blunt-tipped setae with or without sockets. Some of the short setae are shown to be innervated and their walls contain numerous pores. Three pore-types can be distinguished: (1) funnel-shaped pores in single-wall setae; (2) slit-pores with coneshaped connections in the second wall to the inner fluid; and (3) spoke canals with a mushroom-shaped connection to the inner fluid in setae with an incomplete second wall. The short setae examined differed from each other in pore structure, number of lumina and innervation. Except for some slight differences in pore structures the ultrastructure of these setae conforms with the descriptions of chemoreceptive (or thermosensory) sensilla found in ticks and insects.