Some paramagnetic resonance experiments on pairs of exchange coupled paramagnetic ions in magnetically dilute crystals are described. The exchange parameters found in this way are compared with susceptibility data for the corresponding concentrated salts. For some iridium salts the exchange energy is discussed in terms of a simple model which uses a Morse potential energy curve. The results emphasize the importance in these salts of superexchange through two intermediate nonmagnetic ions and suggest that similar interactions may be important in other antiferromagnetics.