These printers use the C3903A cartridge:
Click On a Printer to View it's Cartridges
HP LaserJet 5 MP
HP LaserJet 5 P
HP LaserJet 6 MP
HP LaserJet 6 P
HP LaserJet 6 PSE
HP LaserJet 6 PSI
HP LaserJet 6 PXI
Canon LBP VX
Canon Series 5 MP
Canon Series 5 P