Аннотация:A selection of results obtained with very forward detectors of the CMS experiment at LHC is presented. Studies of the energy flow, dE⁄deta, are extended into very forward region with CASTOR calorimeter (-6.6 < eta < -5.2) for pp collisions at 3 different center-of-mass energies (0.9, 2.76 and 7 TeV) and PbPb collisions at 2.76A TeV. Results are compared to hadronic interaction models as implemented in standard collider physics generators and generators used in cosmic-ray physics.