A 2 year research program was devised to examine the major issues associated with testing hearing protective devices (HPDs) in laboratory environments and applying the results to actual protector usage in the industrial field setting. Four groups of ten subjects who were nonusers of HPDs prior to entering the study were assigned to one of four HPDs. The laboratory protocol used simulated the effects of HPD wearing time, activity movement, and two fitting conditions on attenuation afforded by user molded foam and premolded earplugs, a foam cushion earmuff, and a combination of the earmuff worn over the foam earplug. The first study used the same testing procedure, fitting conditions, and three HPDs as in the laboratory study, plus an additional ear canal cap, and determined the actual noise attenuation obtained over two consecutive 3 week periods of HPD use in the workplace. The laboratory attenuation results on the average obtained after the subject underwent the work activity tasks overestimated the field performance by 8.3 decibels (dB) and 5.7dB for the foam plug, and by 10dB and 6dB, respectively, for the premolded plug. In contrast, the laboratory results provided much better predictions of field protection for the earmuff. Close examination of the data suggested that a naive subject fit protocol in the laboratory may yield attenuation results closest to that of well trained users in the field.