Pseudothrombocytopenia may have any of a number of causes, one of which is agglutination in vitro. This phenomenon was found in samples of blood from six patients. A serum factor responsible for the agglutination was demonstrated. The factor was dependent upon the presence of EDTA and was more active at room temperature than at 37 C. It could be identified as an IgM immunoglobulin in four cases. In the other two cases definite characterization was not possible, but there was some evidence in favor of an IgM factor. All six patients had elevated serum IgM levels, but they had different and unrelated clinical disorders.

Summary A programmable system, the Textur Analyse System (T. A. S.) of E. Leitz, is described for use in interactive work on pattern recognition of white blood cells. The system appears well suited for the task of finding new parameters for the characterization of normal and abnormal blood cells. Hardware advantages such as speed of operation are coupled with software flexibility. The first application of the machine has been the extraction of some of the ordinary parameters for characterization of leucocytes. The value of each parameter has been analysed with the interactive statistical pattern analysis program (ISPAHAN). A separation in the five normal classes of peripheral white blood cells can be achieved, in which the nuclear/cell area ratio and nuclear area together with the density histograms proved to be the most important parameters. The interesting feature of the system is, however, the possibility of finding new data for the recognition of normal and abnormal blood cells.

Summary. The characteristics of large, abnormal cells in the peripheral blood of patients with Hodgkin's disease have been investigated with cytochemical stains. It was possible to distinguish clearly cells of the granulocytic series, megakaryocyte parts, cells of the mononuclear phagocytic system and immunoblasts. These cells, however, are not specific for Hodgkin's disease, for they could also be found in normal subjects, in patients with infectious mononucleosis or cytomegalovirus disease and patients with lympho‐ or reticulosarcoma. Cells considered to indicate dissemination of Hodgkin's disease could only be detected in the peripheral blood of patients with this condition, and not in the other diseases mentioned above. These cells do not react with the periodic acid Schiff stain, Sudan black, peroxidase, non‐specific esterase and sometimes faintly with methyl green pyronin. It is therefore improbable that these cells belong to the categories of the granulocytic or monocytic cells, but a relationship to the lymphoid cells on the one hand or to the reticulum cells on the other could not be excluded on the basis of this morphological investigation.

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