Abstract The principle of fluoride determination by diffusion of hydrogen fluoride in Conway-type cells made of polypropylene has been applied to the determination of fluoride in plasma, liver, muscle, calcified tissues, urine, and saliva. Methods for preparation of the low fluoride containing biological specimens by precipitation of proteins with perchloric acid and analysis of the supernatant liquid are described. The results of fluoride analyses by diffusion compare well with those obtained by microdistillation. The diffusion method for fluoride analysis is more simple than distillation procedures.