We report a null detection of 12 C O emission from a sub-condensation in a High Velocity Cloud (HVC). As a consequence of this, an upper limit of n ( H 2 ) X ( C O ) D V / D R ≤ 2 × 10 − 5 was set. This implies that 12 C O abundance is deficient by at least a factor of 10 if the HVC is predominantly molecular, otherwise the CO abundance of the HVC might be normal.