A parallelism test was performed to verify the good binding affinity of the testosterone antibody of the assay in water vole. The plasma of four male voles were serially double diluted (From 1:2 to 1:4 for sample 2 and 3 and from 1:2 to 1:8 for sample 1 and 4). The graph shows a good parallelism between the standard curve and the curve of the serial double diluted samples tested.