In investigations concerning the influence of stimuli emitted by chickens on the host-finding behaviour of hungry female adult Argas walkerae ticks, we found that 92.5% of the ticks migrated to the stimulus source following their simultaneous exposure to odours and to a CO2 gradient increasing in the direction of the chicken, as opposed to 67.5% following their exposure to kairomones of chickens in the absence of CO2. Migration of the ticks toward the stimulus source was precipitated by a wide range of CO2 concentrations (varying from 0.06 to 1 vol% within the odour mixture) but always required an increasing CO2 gradient in the direction of the chicken, whereby differences in concentration of 0.01 vol% over a distance of 2.5 cm were sufficient. During exclusive confrontation with either CO2 or heat in a gradient otherwise analogous to that emitted by a chicken, only 27.5% and 55% of the female ticks migrated to the stimulus source, respectively. Accordingly, odours emitted by chickens are considered to represent an essential stimulus modality, whereas body heat and CO2 are regarded merely as secondary, non-specific stimulatory agents. Investigations involving the exposure of ticks to a habitat similar to a chicken roost revealed that host seeking and finding are not influenced by gravity and occur only in darkness and that the portion of host-finding ticks diminishes with increasing distance from the blood donor.