On 11 September 2000, a NASA ER-2 aircraft underflew the Terra spacecraft during the Southern Africa Regional Science Initiative (SAFARI) 2000 field experiment. The Scanning High Resolution Interferometer Sounder (S-HIS), Moderate Resolution Imaging Spectroradiometer (MODIS) Airborne Simulator (MAS), and Cloud Physics Lidar (CPL) instruments onboard the ER-2 have provided a data set for a first look at the accuracy of the Collect 3 (L1B Version 3.X) Terra MODIS L1B radiances for the thermal infrared (TIR) bands. Based on comparisons between MODIS and S-HIS nadir viewing data and an estimation of the existing uncertainties, the radiances of most MODIS TIR bands are found to be very near or within specification. There does not appear to be a significant influence by electronic cross talk on the midwave IR (MWIR) bands for the low reflectance, flat thermal scenes used in the evaluation. Longwave IR (LWIR) split window band residuals are within 0.1 K with an estimated uncertainty of ¿0.13 K, raising confidence in their accuracy. Midtropospheric water vapor band residuals are also within specification, despite known detector striping in these bands. Residuals in the LWIR upper tropospheric CO2 bands 34--36 exceed specification. However, these are not considered strong indications of L1B performance issues due to possible undocumented uncertainty in the altitude correction for the unmeasured atmosphere above the ER-2 aircraft level.