The technological opportunities offered by web-based surveys allow to track precisely the behaviour of each respondent while filling in a web questionnaire. The log files created by a web-survey server system can provide factual information about the on-line response process: how the respondent navigates from one screen to another, how many times the printable version of the questionnaire is downloaded, how many questions are answered, how long the response process takes, etc.. In this framework, detailed log data related to the Italian business Research &
Development survey are analysed in order to identify possible critical aspects in the questionnaire design and improve the accuracy of responses. Some indicators describing the behaviour of the respondent companies are proposed. Results from log data are reported by path and discussed. Besides, they are merged with statistical information coming from other sources, including the Italian register of active enterprises.