Nail biopsy is an important element in the diagnosis of ungueal mycosi
s. The biopsy is taken from the distal extremity of the nail which is
not sensitive, so no anaesthetic is needed. The sample is then immerse
d laterally into paraffin and cut into thin pieces colored by a simpli
fied PAS. Then it is possible to observe the fungal elements in the in
terior of the keratine and to determine the nature of the pathogenic s
pecies. This simple and rapidly performed technique is very useful. It
can be executed systematically when cultures have remained negative e
ven though fungal elements have been seen under direct examination or
in cases when yeasts or moulds with a doubtful pathogenic role have be
en isolated.