The Harris County Gravid Trap (HCGT) used for West Nile virus (WNV) surveillance from 2003-06 is described. The HCGT collected 1,918,483 Culex quinquefasciatus females (over 36,627 periods), with 466,296.37 (8,452.74) yearly. Only 48,094 Aedes albopictus females (over 15,139 periods) were collected, with 10,277.79 (3,260.33) yearly. The highest mosquito production occurred in July for Cx. quinquefasciatus (63,851.25 +/- 0.13), and for Ae. albopictus (2,981.80 +/- 0.09). Integrating gravid traps within our program has increased our ability to detect WNV efficiently in both species.