Web Services have enabled businesses and organizations to collaborate without platform interoperability and programming language barriers. Quality of Service (QoS) of a web service is an important factor that differentiates similar services offered by different service providers. Such a measure would allow web service clients to choose and bind to a suitable web service at run time (based on QoS attributes). Some researchers have proposed the integration of the QoS measure on the web service directory server. However, a mechanism to maintain the QoS metric has not been defined yet. In this paper, we propose such a mechanism. This mechanism involves automated measurement of QoS attributes on both the client and provider sides, when the service is being used, and updating the QoS-aware web services directory with this information. We describe a prototype we developed for this purpose and present the results of using this prototype for gathering QoS measurements at run time.