Figure 6: The Ferguson-Robertson Method. Mean (n=6) concentrationresponse curves on guinea-pig atria for isoprenaline in the absence () and presence (♦) of a maximum concentration (9 x 10-6M) of prenalterol. The increases in rate in the presence of prenalterol, R(A+B), are measured either above the prenalterol-induced rate eB or above the maximum pre-prenalterol resting rate (eA - eB) (Fig. A) and expressed as a percentage of the maximum. The dose shift for equieffective responses now gives the classical dose-shift 1 + KB/ [B] (Fig. B). ¨