This mini-review discusses how soft sensors can contribute to accomplish FDA's process analytical technology (PAT) ambitions in the manufacture of bio-therapeutics. Focus is on applications with protein-based drugs (proteins, antibodies), but also gene therapy vectors as well as cell cultures are considered where chemical and bio-analytical as well as mathematical and statistical methods are used as tools. An overview of existing soft sensor alternatives and how these can be configured to meet typical industrial needs is provided. It is noted how several of these needs coincide with the PAT regulatory incentives but do also address process economic aspects of bio-therapeutic manufacture. Evaluation of soft sensor alternatives is highlighted in relation to the production targets, quality attributes and the specification of these as well as shortcomings and needs for further improvements. (c) 2014 Society of Chemical Industry