de la vitamine D:! en solution pure et en pr6sence cle sels calciqires par V. LASAREFF (Liege) et E. V. ROUlR (Gembloux) SLXMA~<> , --'I'ht, sc.iisitivit) ol ii direct specl rophi~t~nietrir tlciterrnination of vitartiin D,, (calciferoll, ]lased on its ultra-violet absorptiori. proved to be 1 microg~am/ml., or better. Compared with the currenl colorimetric trchiiiqtres, the ultra-violet method is capnble of a much higlicr ;Iccuriicg.--Thr ultra-violet absorption spcctrum o f calciferol rcmaiii1; tii~chiiiiged in the prcsencc of calcium phosphate or gluconntc?. The lattor conipouiids show only a slight rontinuous absorption in the ~m c spi~,l r;il range. Coiiscquently. fhc iiltra-violct determination of i:;~lcjf~~rfil t'nil Iw pt~forinc~tl without j)revinus climiiialiori of calciuin qalts.