The number of networked multimedia applications is increasing, therefore users' quality requirements need to be clearly specified. At present, subjective assessment is used to do this, however it has drawbacks when used in isolation. Therefore, this research approach is utilising physiological indicators of stress to measure the impact of media quality on users - this is defined as user cost. Four studies using this technique have shown that physiological responses to audio and video degradations can be detected and that they do not always correlate with subjective results. Subsequently, a three-tier approach to multimedia quality evaluation is proposed, which incorporates task performance, user satisfaction and user cost.