This paper presents results about the determinants of export behaviour of services firms. Using a unique panel of enterprises for the years 2003 to 2005, the impact of size, productivity, human capital, experience on the national market, etc. on export behaviour are analysed. In addition, the researchers control for unobserved time- invariant characteristics by using a pooled fractional probit estimator. When there is no control for unobserved time-invariant heterogeneity the overall results are in line with previous studies. When there is a control for unobserved effects, the positive effects of productivity and human capital disappear, and only size has a positive significant effect.