Objective-To study chronic eVects of hydrogen sulphide (H 2 S) on cranial nerve I (nervi olfactorii), which have been only minimally described. Methods-Chemosensations (smell and taste) were evaluated in eight men who complained of continuing dysfunction 2-3 years after the start of occupational exposure to H 2 S. Various bilateral (both nostrils) and unilateral (one nostril at a time) odour threshold tests with standard odorants as well as the Chicago smell test, a three odour detection and identification test and the University of Pennsylvania smell identification test, a series of 40 scratch and sniV odour identification tests were administered. Results-Six of the eight patients showed deficits of various degrees. Two had normal scores on objective tests, but thought that they continued to have problems. H 2 S apparently can cause continuing, sometimes unrecognised olfactory deficits. Conclusion-Further exploration into the extent of such problems among workers exposed to H 2 S is warranted. (Occup Environ Med 1999;56:284-287)