In October 2003 a residential demand study was conducted for Downtown, Midtown and the Texas Medical Center.  The study shows an aggregate demand for 16,400 units now. 

According to the study, "Consistent with the findings of the 1993 and 1998 surveys, there are two prime target markets for Downtown/Midtown renters and buyers -- high-end renters paying $1,000 or more per month ... and Downtown/Midtown/Texas Medical Center employees other than those already accounted for as high-end renters...."

The study, conducted by CDS for the Houston Downtown Management District, can be accessed here. 

Residential Demand Study