In animal and man, chronic intoxication with vitamin A or retinoids may be responsible for vertebral hyperostosis and periosteal appositions. Vertebral hyperostosis is found in hyperostotic disease but also in the course of ankylosing spondylarthritis. Therefore, we felt it would be interesting to study blood retinol levels in 22 patients with hyperostotic disease, 29 patients with ankylosing spondylarthritis, 18 patients with rheumatoid polyarthritis and 21 reference patients. The Kurskal-Wallis test has demonstrated a significant difference of blood retinol levels between these four groups (p less than 0.0001). The blood retinol level was more elevated during hyperostotic disease (3.63 +/- 1.13 mumol/l) than in the reference group (2.94 +/- 0.76) and was, on the contrary, lower during ankylosing spondylarthritis (2.57 +/- 0.66) and rheumatoid polyarthritis (2.32 +/- 0.64). This study confirms the elevation of blood retinol during the course of hyperostotic disease; such a abnormality was not demonstrated in the course of ankylosing spondylarthritis, and on the contrary, suggest that a decreased blood retinol level may be observed during chronic inflammatory rheumatic diseases such as rheumatoid polyarthritis or ankylosing spondylarthritis.