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We will present HST/GHRS spectra of 9 low mass PMS stars. All 7 classical T~Tauri stars show evidence for H$_2$ Lyman band emission lines. Emission in the Lyman band arises from either shock-excited gas or in gas at temperatures of 2000-4000K. In the latter case, the emission can be used to probe the innermost portion of the circumstellar gaseous disks (within about 10 stellar radii).
Comparison of large and small aperture spectra show that all the H$_2$ emission from T~Tauri arises within 15~AU of the star. Two naked T~Tauri stars, with ages of $\sim$2~Myr, do not show evidence of H$_2$ emission. This has implications for the clearing times of the gaseous components of the circumstellar disks of PMS stars.
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