The 2DEG in CdTe/InSb heterojunctions has been investigated using magnetotransport and far-infrared magnetotransmission measurements. Two series of oscillations are seen in the Shubnikov-de Haas effect; however, a comparison of the parallel field magnetoresistance with the universal curves of Reisinger and Koch indicates that six subbands are occupied, and that the total carrier density is around 4.7 × 10 12 cm −2. A broad cyclotron resonance is observed in the magnetotransmission, yielding an effective mass of m ∗ = 0.045m e . This is consistent with theoretical predictions for electrons in InSb inversion layers with a carrier density close to 5 × 10 12 cm −2. Published data on other similar systems will be discussed in the light of these measurements.