In the so-called ‘‘plate incorporation test’’ in which the PEEK raw material is finely cut and applied direct to the agar plate without the addition of solvent there was, as expected, no evidence of cytotoxic or mutagenic effects. In the HPRT test there was a significant increase in the number of mutants per dish, both after addition of N-acetylaminofluorene and N-methyl-N0-nitro-N-nitrosoguanidine (with and without an external metabolic activation system=7S9), but not after treatment of the cells with PEEK-DMSO-eluate. This means that the PEEK material under study did not release any substances that cause V79 cells to mutate. The investigation of the toxic reaction on the material under study revealed that the number of surviving colonies per 105surviving cells lay within the range of or below the solvent control even in the presence of high PEEK concentrations (5.0 mg/ml). Therefore, in summary, the study produced no evidence of cell damage caused by PEEK.