The on-line analysis of operational data and prediction of furnace irregularities, though difficult, are essential for the improvement of the control of blast furnace operation. Three models based on artificial neural networks for the recognition of top gas distribution, distributions of the heat fluxes through the furnace wall, and for the prediction of slips have been designed. The off-line test results showed that a trained perceptron network could recognize various types of top gas profiles. A classifier consisting of a self-organizing feature map network and a learning vector quantizer could classify the characteristic patterns of heat flux distribution; and a model based on a back propagation network could properly predict the probability of upcoming slips in advance. The most important operational variables needed for predicting slips have also been extracted. It has been proved that the neural network used has a good capability of predicting furnace irregularities.