A-11 USE OF NEURAL NETWORKS IN LOG'S DATA PROCESSING – PREDICTION AND REBUILDING OF LITHOLOGIC FACIES Abstract 1 When a log is missing in a drilling hole geologists hope to deduce it from others logs available in another part of the hole or in a neighbouring hole in order to define the lithologic facies of the hole. This paper presents a neural network method to predict the missing log's measure from the others available log's measures. This method based on Multi-Layer Perceptron (MLP) acts as a non linear regression method for the prediction task and as a probability density distribution