Non-Magnetic drill collars have been developed to meet requirements of magnetic permeability, strength and galling resistance. Until recently, corrosion resistance has been treated as a secondary consideration. This paper describes recent developments in corrosion resistance in these applications, and the results of comparative testing, using Critical Pitting Temperature testing. Corrosion resistance generally correlates well with chemistry, and the CPT identifies exceptional cases quite clearly. Recent developments in drill collar materials have markedly improved their corrosion resistance.