Nowadays nickel is a global problem, related to occupations (mainly 
metalworkers) and to life habits. The dietary intake, more than environments, is 
the source of a basic immune identification and also of possible complications 
after occupational inhalation or contact. Nickel insoluble compounds are proved 
to be cancerogenic. Nickel ions are very reactive with proteins and oxidant, 
then also potential irritant for the airways. Metallic nickel and soluble 
compounds are sensitizers, causing dermatitis, rhinitis and asthma. Recently a 
Systemic Nickel Allergy Syndrome (SNAS) has been identified in allergic 
subjects, with a clinical picture of urticaria, general hitching, headache, 
gastrointestinal troubles. SNAS may affect allergic occupational or 
non-occupational ones. Studies are in progress aimed to an oral treatment 
inducing immunotolerance. Nickel in urine seems to be the best tool for 
monitoring nickel absorption.