Morphological comparative study of the normal anatomy of the internal mammary artery, coronary artery and renal artery, and their atherosclerotic alterations. We report in this paper the comparative results of a morphological and morphometrical study of the normal anatomy of the Left Coronary Artery (interventricular descending branch) (LCA), Internal Mammary Artery (IMA) and Renal Artery (RA) and their atherosclerotic alterations in 27 unselected people of both sexes aging from 19 to 76 years (average 59 +/- 14.3). Sections from three different segments of each vessel were examined by measuring the thickness of the intima and media calculated at the maximum intimal thickening. The lumen was also measured at the level of its highest pathological reduction; the same measurements were carried out on sections free from atherosclerotic damage. Then the intima to media ratio was assumed as major indicator of atherosclerosis involvement according to the literature. All these parameters were statistically analysed. With these procedures we found that LCA displayed more severely atherosclerotic changes than IMA. The degree of damage in RA fell in between when compared to the other arteries. The intima to media ratio average was 0.061 mm. (+/- 0.084) in I.M.A.; 0.882 mm. (+/- 0.753) in L.C.A. and 0.272 (+/- 0.315) in RA with statistically significant differences between IMA and LCA (p less than 0.001) and between IMA and RA (p less than 0.001). In the lesion free sections intima to media ratios were 0.178 (+/- 0.90) in LCA, 0.053 (+/- 0.28) in IMA and 0.082 (+/- 0.127) in RA. The difference was statistically significative between LCA and IMA, but not between RA and IMA.(ABSTRACT TRUNCATED AT 250 WORDS)