The effect of various metals and PHA on the proliferation rate of patients’ leukocytes. The effect of various metals (Ti 0.01 mM, Co 0.1 mM, Cr 0.1 mM, Ni 0.1 mM) and PHA (0.1 mg/ml) on the proliferation rate of patients’ leukocytes in group 3 is shown. Cells were untreated or treated as indicated. (a) (unreactive), it is clearly demonstrated that metal challenge did not influence cellular proliferation before and after the surgery. (b) (reactive), however, Co, Cr and Ti increased the proliferation rate significantly 6 months after surgery in 25% (10 patients) of group 3, which was increased up to 35% (14 patients) after 36 months, distinguishing a subgroup referred here as metal sensitive patients in group 3. Positive control PHA increased proliferation significantly in each experiment. Columns represent means + SD, level of significance is shown, *p < 0.05. Note that Ni did not influence proliferation significantly.