Over 80 pct of domestic phosphate rock, which is the starting material for phosphorus-containing fertilizers, comes from central Florida deposits. As higher grade deposits are depleted, lower grade phosphate ores containing mgo in the form of dolomite are encountered. Treating high-mgo ores with present beneficiation technology will not yield a concentrate meeting specifications for acidulation. The Bureau of Mines conducted research on three high- mgo phosphate samples from south Florida. The samples contained, in percent, 5.4 to 10.2 P2o5, 1.9 to 7.6 Mgo, and 35.3 to 60.1 Acid insolubles. A technique of sizing, grinding, desliming, scrubbing, and redesliming was used to produce a feed suitable for continuous flotation studies. A conventional fatty acid-fuel oil rougher flotation followed by two to three cleaner stages resulted in concentrates containing, in percent, 30.7 to 31.3 P2o5, 0.6 to 1.3 Mgo, and 2.5 to 4.8 Acid insolubles. The p2o5 recovery from the flotation feed ranged from 55.1 to 89.7 pct.