The need to measure and assess the electronic information made available by the Web has given rise to the development of indicators that can be used to evaluate the final quality of this information. Web spaces of the informational units, which include virtual university libraries, are prime candidates for such a process of assessment. The present study has a look at the quality of the informational services supplied by virtual university libraries in Spain, adopting as the variable of analysis the evolution that certain quality indicators of a formal character have exhibited over an exemplary period of six months. The interpretation of our results makes manifest an overall satisfactory evolution, though the breakdown by regions or Autonomous Communities of Spain reveals deficiencies in some cases.