Audience research by means of surveys has a long tradition, certainly within arts and humanities oriented research. Yet, due to selective sampling and unit nonresponse it frequently lacks the methodological rigour to make scientifically valid statements based on sample estimates. This is one of the first attempts to explore unit nonresponse in audience research. More specifically, it focuses on the explanation of nonresponse by the socio-demographic and more topic related characteristics of a theatre audience. Using a two-step procedure for the on-site collection of data, the characteristics of respondents are compared with those of nonrespondents. In step 1 the composition of the theatre audience is compared to a proxy of a theatre population benchmark based on a weighted sample of the Flemish population (APS-2000). The validity of this best available method is discussed. Step 2 compares respondents with nonrespondents on a micro-level: ignoring unit nonresponse in step 1, we use logistic regression to map selection in step 2. The chance of cooperating with the survey has been found to increase with educational attainment and vary according to occupational category. Moreover, involvement with survey topic is confirmed as a strong predictor of survey participation. Gender, age and experience with theatre remain insignificant in predicting response behaviour. These findings are compared with the socio-demographic correlates of response behaviour in general populations. Implications for statistically controlling for nonresponse bias in audience research are discussed. Suggestions for further research are presented.