We present new observations of the merging system Arp 299 obtained with the IRAM Plateau de Bure interferometer. We have observed the 12CO(1 − 0), 12CO(2 − 1), 13CO(1 − 0) and HCN(1-0)lines. For the 12CO(1 − 0) line, short spacings were recovered by using 30m data; about half of the total flux is found in weak and extended emission filtered out by the interferometer. The 12CO(1 − 0)map shows th...