Lack of specificity of the AE7A5 anti-Epo antibodies. Four urine samples (lanes 1-4), obtained from the same athlete on 4 different days immediately after a 4 × 1000 m sprint, were concentrated 20-fold by ultrafiltration and subjected to immunoblotting after SDS-PAGE with monoclonal (clone AE7A5) anti-Epo antibodies (left blot). The right blot was treated identically except for the absence of anti-Epo antibodies. The protein concentration in the nonconcentrated samples amounted to 1.2 (lane 1), 1.1 (lane 2), 0.47 (lane 3), and 0.9 (lane 4) g/L.