OBJECTIVE In earlier studies [see literature (2, 20, 21, 22)] observations concerning the effect of Solanum Melongena (Sol. Mel.) (violet egg plants) on experimentally induced artheromatosis in rabbits were reported. This study aims to investigate histologically the effect of Sol. Mel. on experimental atheromatosis in mean-term (2--4 weeks) and long-term (8--12 weeks) tests. METHODS For details of the test arrangement see AUBOCK and MITSCHEK, Exp. Path. 9, 323--335 (1974). From one portion of the material for histological examination cryostat sections were prepared, the other portion was fixed in Bouin's solution or in Baker's formol and paraffin-embedded at 58--60 degrees C (cross sections of the aorta). The specimens were stained as follows: erythrosin in conjunction with haematoxylin; aqueous or alcoholic solutions of toluidine blue (pH 3.5 to 5, and 7); methylene blue (pH 2.5 to 5, and 8); alcian blue (pH 2.5); Schiff-PAS; alcian blue and PAS in combination; Sudan III; elastica-van Gieson (blue) and Weigert's iron haematoxylin. For demonstration of mucopolysaccharides (MPS) the control sections were pretreated in a 10% Takadiastase solution for 10 minutes at 37 degrees C. In liver sections PAS-reactivity was additionally blocked by dimedone (cyclohexanedione) for elective demonstration of glycogen. The tissue sections were studied in transmission--, incident- and dark field illumination. RESULTS lipid deposits as demonstrated by surface preparation technique could not be seen in paraffin sections after just one day. In the vascular wall histological changes were earliest visible after 10 to 14 days (enlargement of the subendothelial space and honeycombed edema with fine dispersed lipids). At this stage a "haematoxylin-effect" did yet not develop. Sometimes these alterations were also present in the upper layers of the media. They always first occurred in the aortic arch. At this time the Sol. Mel.-treated animals of group II only occasionally developed superficial edemas. Enlargement of the media with edematous infiltration and loosening of the elastic fibers was similar in both cases (figs. 1a and 1b). Fatty degeneration of the liver was already macroscopically visible on day 14; in untreated animals of group I it was more expressive than in group II (figs. 2a and 2b) -- this likewise applied to the cholesterol content (figs. 3a and 3b). After about 30 days in group I the earliest macroscopically visible plaques occurred prevailingly in the aortic arch and in the thoracic aorta. The development of such small foam cell plaques could be continuously observed with a hand lens (fig. 4a). In group II, however, it was not possible to observe any development of plaques with a hand lens, persistence of edemas was demonstrable with such (fig. 4b). Within these, fine dispersed droplets were present (fig. 5) but exact localization was only possible by electron microscopy [see literature(2)].