BACKGROUND: Protein A chromatography fouling is accompanied by two major events, one is the loss of protein A ligands and other is fouling due to non-specific, irreversible interactions of foulants with resin particles. This paper presents implementation of process analytical technology based control for fouling of protein A chromatography resin using a novel, fluorescence based approach. This approach enables direct, in situ measurement of protein A ligand density as well as monitoring of resin fouling during resin reuse. RESULTS: A novel, fluorescence based process analytical technology (PAT) tool has been designed and used for screening a variety of cleaning protocols. A two-step cleaning protocol was created using this methodology. The above mentioned fluorescence based approach was successfully used to monitor fouling and to take a decision on when to initiate cleaning. This resulted in effective maintenance of dynamic binding capacity and step yield at 50 cycles (DBC:97% of the original value vs 65% with conventional protocols and yield: 93% of the original value vs 73% with conventional protocols) and at 200 cycles (> 90% of the original value). CONCLUSIONS: The proposed fluorescence based approach has been effectively used for monitoring and control of resin fouling upon reuse, thereby resulting in a substantial increase in resin lifetime. (C) 2017 Society of Chemical Industry