Measurement of oral malodor is complicated by a variety of parameters including complexity of gaseous molecular species, sampling difficulties, temporal variations, choice of suitable subject populations, and lack of agreement on reference standards. Since oral malodor is a perceived olfactory stimulus, direct sampling and assessment by human judges may be the most logical measurement approach. However, as with other psychophysical assessments, human malodor measurement by the human nose may vary widely among and between judges, and consequently cannot be confidently reproduced in other laboratories. Such shortcomings have led several investigators to propose quantitative approaches based on measurement of volatile sulfide compounds which are associated with oral malodor. Highly sensitive and discriminatory measurements of volatile sulfides can be made using gas chromatography although for rapid sampling of larger subject populations, portable sulfide monitors may be more appropriate. Future research in this field should consider: 1) improved and simplified instrumentation for more rapid through-put and reliability; 2) development and definition of reference standards for oral malodor assessment; 3) formulation of clinical studies with appropriately sized, well-defined patient populations; and 4) further development of within mouth, site-specific measurements.