A bioassay or biological assay is a biological testing procedure for estimating the concentration of a pharmaceutically active substance in a formulated product or bulk material. In contrast to common physical or chemical methods, a bioassay results in detailed information on the biological activity of a substance. Over the last decade bioassays and biostatistical analysis have become more important in effectively controling the quality of biopharmaceutical development and manufacturing.
The general approach of most bioassays is to perform a dilution assay, which measures the biological responses at several doses. A key assumption of a dilution assay is that the active component follows the same principle of activity in standard and in sample preparation. In this case the unknown preparation may in theory be derived by diluting it with inert components or by concentrating the bulk solution. This concept of similarity may be monitored by using the parallel-line model (parallel-line assay) or the parallel-logistics models. Additionally, slope-ratio and dichotomous assays (quantal response assays) are available as well.
All methods are suitable for analysing the results obtained by several biological assays. Examples of these assays are given below: