F. H. Comhaire Many diseases were, at the beginning, merely defined by the description of their clinical appearance. Next, the pathogenic mechanisms underlying the diseases were recognized. Since then, the proof of presence of the pathogenic agent or agents has been required to confirm the diagnosis. However, it sometimes happens that the pathogenic agent can be demonstrated without the disease being clinically evident. Confusion arising from this observation may cause endless, often purely emotional discussions between "believers" and "non-believers". Moreover, if the disease involves potential disturbance of male fertility, the problem is further obscured by the difficulty of defining man''s fertility. Indeed, during the short history of andrology, the criteria for judging a man and his ejaculate as potentially fertile or infertile have repeatedly changed. Andrological "landmarks" in general do not hold up for long, and some scientists continue to set themselves the task of proving the "old" definitions invalid. Certainly, such developments are necessary to make science more exact and to improve medical care. However, while this research is being done, the male partners of barren marriages continue to seek advice and treatment. Common sense and an empirical approach in the handling of these cases may result in obviously encouraging results, which non-believers will ascribe to "witchcraft" and believers will see as confirmation of their opinions.