We report two cases of asthenospermia, which appeared to be associated with exposure to histamine H1 receptor antagonists. A 44-year-old man and a 35-year-old man had continued the treatment with fexofenadine hydrochloride and cetirizine hydrochloride, respectively, under the diagnosis of hay fever. They and their wives had been examined as infertile couples. Infertility evaluations revealed no problems with their wives; the patients, however, were found to have a low sperm motility (<10%). On suspicion of adverse effects of the histamine H1 receptor antagonists, they stopped treatment with these drugs, which resulted in a complete reversal of spermatic dysfunction. Current information identifies the potential fertility hazards of histamine H1 receptor antagonists.