The safety and toxicity of chemicals given first to animals and finally to humans are generally estimated with a method of safe coefficient

which is scientifically a way lack of grounds. To make a change of the old method

we designed a Physiologically Based Pharmacokinetics Medel for the estimate of safety and toxicity of chemicais. As an example

p-nitrophenol sodium （PNP-Na） is used in the research work. Studies of the PNP-Na pharmacokinetics in bodies of rat as well as humans are made

and possibilities of making use of the Model in the estimate of safety and toxicity of chemicals are discussed.