Nicotine causes many dangerous effects in different levels to many species and form many histopathological changes. It is metabolized primarily by the liver, and to a lesser extent, the lung and kidney. Nicotine is responsible for the shrinkage of male reproductive organs. It is also responsible for decrease in the level of testosterone, destruction of sperms, decrease sperm motility, relative infertility and impotence in males. Many histopathological changes have been seen in the testis of mice in this work with decrease in the weight. This book highlights the damage of nicotine to the testis and the raeson to infertility. It tells the causes and recommends the ways to avoid its use in Pakistan.