THE availability of highly purified rare earths, elements 21 and 58–71, has stimulated interest in their chemical and physical properties1. Haley et al.2–6 have examined their biological effects and reported that although they can produce non-specific liver damage they exert their greatest toxicity on the ocular and dermal tissues. However, even this damage can be repaired with time and results in no permanent injury. Recently, it was observed that the intradermal injection in guinea pigs of 0.05 ml. aqueous solutions of 1 × 104−1 × 106 concentrations of praseodymium, neodymium, europium, dysprosium, hol-mium, erbium or lutetium chlorides resulted in the formation of 2-mm diameter nodules containing crystalline deposits (Fig. 1). Observation for periods of 45 days showed no decrease in nodule size or any resorption of the crystalline deposits.