The Instability index is a measure of proteins, used to determine whether it will be stable in a test tube.

If the index is less than 40, then it is probably stable in the test tube. If it is greater (for example, enaptin) then it is probably not stable.

• Guruprasad K, Reddy BV, Pandit MW (1990). "Correlation between stability of a protein and its dipeptide composition: a novel approach for predicting in vivo stability of a protein from its primary sequence". Protein Eng. 4 (2): 155–61. doi:10.1093/protein/4.2.155. PMID 2075190.

The instability index is also used to calculate risk in agriculture.