It is essential to have an adequate understanding of the acute toxic effects of a new drug. It may not be necessary however to blindly follow the full classical median lethal assay on every occasion. The LD50 was developed to obtain the maximum accuracy from a modest experimental size. The objective of the study and the limitations of the assay should not be overlooked however and undue precision should not be sought. Methodological aspects including species and maximum and minimum doses will be discussed. Other methods and approaches to acute toxicity will be recommended with a more broad approach to acute toxicity than lethality alone.