Sand flies were collected at a focus of leishmaniasis in Medina County, TX, from April through October 1997 and at a focus in Bexar County, TX, from April 1998 through December 1999. Lutzomyia diabolica (Hall) were collected from April through November with peak abundance in July. The male:female ratio of Lu. diabolica was 1:6.2. Almost all female Lu. diabolica in the collections were unfed. One gravid Lu. diabolica contained 49 ova. Female Lu. anthophora (Addis) were active from February through December with three peaks in abundance suggestive of successive generations. Unfed and gravid Lu. anthophora were collected in about equal numbers. Gravid females contained from 1to 64 ova per female. The male:female ratio was 1:1.8, with male Lu. anthophora collected in all months. One female Lu. anthophora was found infected with Leishmania in July 1999. Lutzomyia texana (Dampf) were collected from April through October with peak abundance in April during 1997. The male:female ratio was 1:1.4, with most females unfed. Two gravid Lu. texana contained 32 and 102 ova. An undescribed species of Lutzomyia was found only at the Medina County site from May through September 1997. Trapping sites four times per month versus two times per month in 1999 did not appear to adversely affect the abundance of Lu. diabolica or Lu. anthophora. There were marked differences in the species composition and relative abundance at the different sites, indicating that the spatial distribution of sand flies is patchy in nature.