Pharmaceutical manufactures are spending more than 10% of their annual gross income for research and development. Pre-clinical studies take 20% of these expenditures and clinical phases take 40%. But only 5% of the substances that have passed the pre-clinical phase successfully will pass the four clinical phases and be approved for usage. Such an outcome explains the low sensitivity and selectivity of test-systems using the laboratory animal as a model of human. These systems are based on widespread theory of the phylogenetic species continuity concept which propose that human and animals have the same sensitivity to the therapeutic and toxic action of drugs. The biochemical species stability concept is less known and postulates the essential interspecies and intraspecies variability on a biochemical level. According to this theory, human material (cell cultures and tissues) should be used as a test-system for drug testing. Clinical epidemiology is the new fast growth discipline which gives evidence for using methods of therapy or diagnostics. It has routine procedures for the quantitative estimation of test-systems and characterizes them by sensitivity, selectivity, and validity. These procedures allow to discard low effective test-systems. Principles of clinical epidemiology can increase successful trials and diminish costs.