An extraction-x-ray fluorescence method is described for the determination of copper, nickel and cobalt in roc s. Matrix effects are eliminated, and the precision corresponds to that of the x.r.f. determination itself. If 500 mg of rock is used, 3–2400 p.p.m. Ni. 3–400 p.p.m. cobalt and 4–1000 p.p.m. copper can be determined with a precision of ±4 p.p.m. up to 100 p.p.m. and ±5% at higher values. One person can determine the 3 elements in 48 rocks in 10 working days. The proposed method should be applicable to other materials.