Within the last years, more and more attention has been paid to the development of on-line monitoring process devices. Particularly, taking into account that the Food and Drug Administration (FDA) launched the Process Analytical Technology (PAT) guidance, which encouraged biopharmaceutical companies to ensure a pre-defined final product quality. On-line sensors are a great opportunity to gather process understanding and to enhance process development. In course of this thesis the usefulness of on-line and in-line measurements to deduct physiological key parameters and accelerate bioprocess development is evaluated using different human embryonic kidney (HEK) cell clones.