The unique properties of rare earth elements (REE) have made them crucial to a number of emerging and growing technologies [medical diagnosis equipment, critical military-based technologies, catalysts, computers, magnets, hybrid cars, windmills etc.] increasing their demand, and strategic importance. Recently, increased demand has led to supply problems, with corresponding price fluctuations and difficulties in obtaining REE for use in the cast iron industry. The anti-nodularising action of deleterious residual elements up to a level corresponding to K = 2.0 (Thielman factor) can be counteracted by REE additions. In relatively high purity base iron in terms of anti-nodularising trace elements (K = 0.7 to 0.8) and 0.04 to 0.05% Mgres, higher REEres contents increased carbide tendency, for both un-inoculated and inoculated irons. A low content of REEres (0.005 to 0.01%) for K < 0.8 is practical and sufficient in a Ca-bearing FeSi alloy inoculated iron. The REE addition from a Ca,REE-FeSi alloy appears to be unnecessary, or even unacceptable, due to the risk of increased chill tendency. The use of a proprietary oxy-sulphide inoculant enhancer, (CaSi-based blend with S, O, Al, Mg) led to a substantial increase in the potency of the Ca-bearing inoculants. It was effective, when utilized in an in-mould inoculation of Mg-FeSi (0% REE or 0.26% REE) treatment, for K = 0.4–0.8. Avoidance of chill (free carbides), control of casting hardness and improved graphite quality parameters were observed with the proprietary oxy-sulphide inoculant.