Three rotational transitions of 12 C 16 O, two of 13 C 16 O, and one of 1 H 12 C 14 N were observed toward the proto-planetary nebula CRL 2688. The spectra reveal a previously undetected wing of emission representing an outflow velocity of about 100 km/s. The mechanical momentum in this wind appears to be too large to be supplied by radiation pressure. Also observed is an absorption feature which is on the blueshifted side of the spectrum with respect to the systemic velocity