Abstract: A shaking water bath suitable for laboratory use comprises a wheeled trolley 12 driven with a reciprocating movement along a linear path between guides 30, 30 by a drive mechanism which includes an eccentric rotary drive member 34 and connecting arm 36. The apparatus is contained in a water tank 16 and the trolley 12 supports a removable tray 14 for carrying receptacles containing the material to be agitated. In one position of the tray 14 complementary abutment elements 50, 52 located respectively on the tray and on the trolley interengage to prevent lateral displacement of the tray. Upon turning the tray 14 through 180.degree. and refitting on the trolley these abutment elements 50, 52 no longer interengage to prevent lateral movement, but a drive pin 56 on the tray then engages with a drive socket 58 in the drive mechanism to cause the tray 14 to be driven with an additional component of motion at right angles to the longitudinal direction of reciprocating movement of the trolley 12.