What are dose-response curves? Dose-response curves can be used to plot the results of many kinds of experiments. The X axis plots concentration of a drug or hormone. The Y axis plots response, which could be almost any measure of biological function. The term â€œdoseâ€ is often used loosely. In its strictest sense, the term only applies to experiments performed with animals or people, where you administer various doses of drug. You don’t know the actual concentration of drug at its site of actionâ€”you only know the total dose that you administered. However, the term â€œdose-response curveâ€ is also used more loosely to describe in vitro experiments where you apply known concentrations of drugs. The term â€œconcentration-response curveâ€ is a more precise label for the results of these types of experiments. The term â€œdose-response curveâ€ is occasionally used even more loosely to refer to experiments where you vary levels of some other variable, such as temperature or voltage. X values are logarithm of doses or concentrations Dose-response experiments typically use around 5-10 doses of agonist, equally spaced on a logarithmic scale. For example, doses might be 1, 3, 10, 30, 100, 300, 1000, 3000, and 10000 nM. When converted to logarithms (and rounded a bit), these values are equally spaced: 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0. If you entered concentrations, instead of the logarithm of concentrations, you can perform the transformation with Prism. Y values are responses In a dose-response curve, the Y values are responses. For example, the response might be enzyme activity, accumulation of an intracellular second messenger, membrane potential, secretion of a hormone, change in heart rate, or contraction of a muscle. You can transform the Y values to new units by multiplying or dividing by a constant. Use Prism’s Transform analysis for this. Transforming to new units will not fundamentally change the results of a curve fit. In some cases, the transform from experimentally observed units to practical units is nonlinear. For example, a nonlinear transform is needed to convert the ratio of two fluorescence values to concentrations of Ca++. Which Y values should be used when fitting a dose-response curve? Nonlinear regression assumes that all scatter around the curve is Gaussian, so you want to use whatever units make that assumption most true. In many cases, this may be hard to know.