The invention relates to a reciprocating piston motor, particularly a refrigerant compressor (1) for a motor vehicle air-conditioner. Said reciprocating piston motor comprises a motor shaft (2), a number of pistons (4), which are mounted inside a motor casing (3) in a circular manner around the motor shaft (2), and comprises a circular swash plate (5), which is driven by the motor shaft (2) and which acts upon the pistons via a linkage assembly (6). The swash plate is connected in an articulated manner to the motor shaft via a driver (7) provided for transferring the drive forces, and the swash plate is mounted on a sliding body (9) in a manner that permits it to pivot about a hinge axis (8) oriented perpendicular to the motor shaft. According to the invention, the sliding body (9) has a recess (9a), which is open toward the rotation axis (11) of the motor shaft and which at least partially encompasses the driver (7) and/or the sliding body (9), on its inner surface facing the motor shaft (2), encloses a cavity (17) inside of which a discharge line (24, 25) passing through the motor shaft (2) leads. The reciprocating piston motor is to be used in refrigerant compressors for motor vehicles.