The evaluation of new therapies to treat allergic asthma makes frequent use of histological studies. Some of them are based on microscope observation of stained paraffin lung sections to quantify cellular infiltrate, an effect directly related to allergic processes. Currently, there is no software tool available for doing this quantification automatically. This paper presents a methodology and a software tool for the quantification of cellular infiltrate in lung tissue images in an allergic asthma mouse model. The image is divided into regions of equal size, which are then classified by means of a segmentation algorithm based on texture analysis. The classification uses three discriminant functions, built from parameters derived from the histogram and the co-occurrence matrix. These functions were calculated by means of a stepwise discriminant analysis on 79 samples from a training set. Results provided a correct classification of 96.8% on an independent test set of 251 samples labeled manually. Regression analysis showed a good agreement between automatic and manual methods. A reliable and easy to implement method has been developed to provide an automatic method for quantifying microscopy images of lung histological studies. Results showed similar accuracy to that provided by an expert, while allowing analyzing a much larger number of fields in a repea- ASTHMA is a chronic inflammatory disease of the lung, characterized by airwayhyperresponsiveness to a variety of stimuli, eosinophilic inflammation of the airways, mucus hypersecretion, and elevated serum IgE levels (1). Mortality of asthma has increased worldwide, despite the use of currently available medications, underlining the need for the development of novel therapies (2-4).Previous studies indicate that murine models are useful for studying allergic diseases, including certain aspects of bronchial asthma such as cellular tissue inflammation and pulmonary function. Three studies are commonly performed in this type of experiments to assess the effects: immunologic parameters (immunoglobulines and cytokines), pulmonary function (bronchial hyperactivity), and histological studies (cellular infiltrate and bronchial mucus secretion). The latter are currently assessed by visual inspection by an expert, as there is no automatic analysis tool available. Such a tool would speed up the process, also providing a more repeatable quantification.In theory, the amount of cellular infiltrate could be accurately assessed by means of an appropriate segmentation algorithm (i.e., border detection) identifying each cell nucleus on the image. The main difficulty for this individual cell segmentation arises from the existence of cell aggregates, which hinders the detection of the contours. This is a difficult task for most image-processing algorithms and the authors do not know of any previous successful attempt. Furthermore, the nuclei of cells in the bronchial wall are similarly stained and have the same size, making it difficult to