Pheromonal enhancement of neurogenesis, sperm density, mammary gland expansion and brain development in the next generation. Compared to defects in vision or hearing, hypo/anosmia (loss of olfactory sense) has received less attention because of its less serious effect on daily life activities compared to blindness or deafness. However, the dysfunction in olfactory sense often accompanies inabilities to appreciate food and to notice rotten food or toxic gas. Thus, studies on olfactory sense may significantly improve the quality of our life. Our physiological conditions are also more affected by the odor of people around us than we recognize. Studies from 1970s have shown that women who live together and spend time together show synchronized menstrual cycles and recent studies have shown that hormone secretions are stimulated by exposure to the odors of opposite sex. In my recent studies, I have found in mice that sperm density is higher in male mice exposed to female-soiled bedding (Koyama and Kamimura 2000) and subordinate males show lower sperm motility (1999).