Acute graft-versus-host disease (AGVHD) is one of the major complications of allogenic non-T-depleted HLA-compatible bone marrow transplantation. It is not yet possible to predict the clinical evolution of the disease at the time of its first manifestation. Twenty patients who initiated the disease with only moderate skin involvement were selected consecutively among those followed between January 1985 and December 1988 in the Bone Marrow Transplantation Unit, Saint Louis Hospital, Paris. A skin biopsy was performed at the onset of the AGVHD for each patient. For each biopsy, one 5-microns thick section was fixed by Bouin's solution, stained with hematoxylin and eosin and studied by image analysis at a final calibration of 7.6 pixels/microns. Ten patients did not exceed grade I (low risk group) and ten developed a more severe grade (high risk group) in the evolution of the disease. The mean and coefficients of variation, skewness and kurtosis of dimension-, form- and texture-related parameters of the nuclei of lymphocytes infiltrating the skin were investigated for their ability to discriminate between the high and low risk groups. The best discrimination was obtained using texture-related variables. An index containing 5 texture-related variables gave the maximum separation between the two groups, with a 100% correct classification. Our results represent a learning-step towards the development of a prognostic index of AGVHD.