This article discusses the series of tests on animal experimental models carried out by our group to evaluate the effect of homeopathic preparations selected according to traditional criteria of pathogenetic similarity. Our overall experience indicates that it is not difficult to carry out experimental studies assaying homeopathic medicines in randomized placebo-controlled tests returning statistically analyzable results. The basic requirement for this purpose is to select validated experimental models. The simplest and most reliable ones are the ones arising from common daily clinical practice or those taken from classical pharmacological studies modified as to fit the goals of a homeopathic assay. By proceeding in this way it will be possible to build a sound body of evidence for the biological effects of high dilutions.