Identical Drives for RAID

I have a server with 3 Western Digital 18Gb 10k RPM hot swappable drives that are no longer being made. The drives are partitioned 2Gb/16Gb With two of the 2 gig partions being mirrored and the three 16 gig partions in a RAID 5 configuration. The hot swap bay has a 5 drive backplane and I would like to add two more drives. Can I subsitute drives from another manufacturer and add them to my RAID 5 set?