The present invention relates to a machine for sealing material in sheets, which have been pre-coated with beads of glue affected by heat, preferably electronically printed toner beads, the beads coming into engagement with each other after folding the sheet into such as the configuration of an envelope or the like, the sheet then being advanced into the machine for adhering the beads to each other. In accordance with the invention, the machine includes a first sealing zone (12) and a second sealing zone (13), which are arranged at 90.degree. to each other with advancing means (36,38, 34,47) for conveying the respective sheet through the sealing zones, each sealing zone having one or more pairs of rotationally driven sealing discs (14,15,18,19,23,26). Each pair of sealing discs includes a first disc (14,15,23) heated by heating means, and a second, preferably freely rotating, disc (18,19,26) engaging against the first disc with a pre-settable pressure. In this way there is heat transfer from the first sealing disc to the second sealing disc so that when a sheet folded to envelope configuration is taken through the machine with the aid of said advancing means, the toner beads situated in this advancing direction are first caused to pass through respectively between said first sealing zone and in that the envelope is then given a new advancing direction at 90.degree. to the previous one, the toner beads in the new direction being caused to pass through the second sealing zone.