This is a proposal for public data sollicited by OTAC to perform additional searches for the H2 pure rotational lines in circumstellar disks around YSO's. Despite their obvious importance to stellar and planetary formation, our quantitative understanding of circumstellar accretion disks -- in particular their radial and vertical temperature and density structure and gas survival timescales -- remains poor. Here we propose to continue the successful observations of the pure rotational lines of molecular hydrogen in circumstellar disks around T Tauri and Herbig Ae stars, started with the open time program GBLAKE.DISKS_H2. These spectral lines, observable only with the SWS aboard ISO, are particularly sensitive to warm, dense gas and thereby provide astronomers with a new probe of the critical 1-30 AU region in potential planet forming disks around young stellar objects (YSOs). Because they arise from the dominant chemical species and have well characterized oscillator strengths, rotational H2 transitions may also provide a direct and unambiguous tracer of the mass in the inner regions of circumstellar disks. Initial observations of the Ophiuchus region show H2 detections in 3 out of 5 objects (van Dishoeck et al. 1997). We propose here a sample of YSO's selected from the Taurus-Auriga, Orion and other regions, coordinated by the PI with the community. Specifically, the selected objects are known to have SEDs from infrared to (sub)millimeter wavelengths that are dominated by emission from the circumstellar accretion disk and not the surrounding cloud material, and complementary millimeter data are available, showing compact emission. The relative H2 line strengths will contain a great deal of information on the vertical and radial temperature profiles, while the overall intensities will accurately constrain the total gas mass in the inner disks for the first time. Combined with stellar evolution models, the ISO data will also bear directly on the gas survival time scales around T Tauri stars. The data will be made public within 1 month of receipt from ESA.