At the age of 12 weeks every kitten should be tested for two very serious feline diseases.  These are the Feline Leukemia Virus (FELV ) and the Feline Immunodeficiancy Virus ( FIV ).  These viruses can be given to other cats you have at home.  Keep the new pet separate from  your old friends until you know that your new pet is negative for these diseases. 

 

If all your pets live indoors then you are all done.  Once you know all your pets are negative for FELV and FIV they are free to mingle and play as they wish.  If your pets go outside ,then they should receive the Feline Leukemia vaccinations before they taste the great outdoors.