The evolution and structure of the atmospheric boundary layer in Houston, TX was examined using radiosonde and tethersonde profiles taken during the 2006 TexAQS II field campaign. The measurements were made from August to October at the University of Houston campus located approximately 1 mile southeast of the central business district of downtown Houston and included twice daily radiosonde profiles and supplementary tethersonde profiles during the nighttime periods. In addition to the regular radiosonde launches, additional radiosondes were launched at 3 hr intervals during special intensive observational periods. Data from these profiles are used to examine the characteristics of Houston's urban boundary layer including the mixing layer height and the depth of the nocturnal inversion layer. Preliminary analyses show that the mixing layer height was variable day to day with heights varying between 1500 to over 2000 m AGL. The top of the nocturnal boundary layer was found to be approximately 150-200 m AGL on most nights.