Following the studies on four compounds, classified in three different groups of toxicity, the validity of the up-down method and the fixed dose procedure was compared to classic Litchfield and Wilcoxon tests. The study was based rather on a very careful clinical observation than on the estimation of animal mortality as recommended in DL50 test. The study showed a considerable consistency between classic tests and the up-down method and the fixed dose procedure. But the determination of acute toxicity of chemical compounds by means of alternative methods proved to be highly humanitarian, and it required much lower number of less suffering animals.