How do you dilute primary antibodies from 1:200 to 1:1000?

To dilute from a ratio of 1:200 to 1:1000, you should perform a 5 times dilution. Divide the desired total volume of the new solution by the dilution factor (in this case, 5) to obtain the volume of initial antibody solution that should be used. The total desired volume minus this number is the volume of dilution buffer that should be added.

For example, if 1 ml of 1:1000 solution is desired, you would add 200 ul of 1:200 antibody solution to 800 ul of dilution buffer.