The seasonal occurrence and diel landing periodicity of Sabethes chloropterus (Humboldt) was studied weekly for 1 yr using the human bait catch in the Pt. Gourde Forest, Trinidad, W.I. Population abundance remained low throughout the dry season (16%) but increased after the onset of the rains in May and peaked by the middle of the rainy season (July-October). The diurnal periodicity of landing was unimodal during the wet season with a major peak between 1200-1600 hours and bimodal during the dry season with peaks at 0800-1000 and 1200-1400 hours. This study documents for the first time the periodicity of landing by Sa. chloropterus at ground level and suggests reasons for failure to detect the yellow fever virus at this level.