Aids:- It is stands for A-acquired. I-immuno D-deficieny S-syndrome. A person who first affected by aids in USA country at 1981. In India the first person affected by aids in 1986 (Chennai) Agent of Aids- Aids cause by HIV virus (Human immunology deficiency virus). This virus are retrovirus means produce DNA from RNA. HIV virus destroyed our T Helper cell which cause immune deficiency .HIV virus produce DNA from RNA by reverse transcription. Transmission of HIV:- a. By sexual contact:- Friends we already discuss about which types of diseases are spread from sexual contact. When we change our partner then we must use condom to protect from HIV and other sexual transmitted disease.this is one of the most reason to transmission of HIV. b. By sharing infected needle:- When we use infected needle then the transmission of HIV chances increases because HIV is spreading from our blood. Some peoples are drug addict and they use