What is the minimum number of cells or minimum amount of tissue that can be efficiently processed with the RNeasy mini kit?

In QIAGEN labs we have successfully isolated RNA from a minimum of 100 HeLa or Jurkat cells without carrier RNA. The Lowest amount of tissue we have used is 0.5 mg. The quality and quantity was verified with RT-PCR. When added to lysates from very small samples, the carrier RNA may in some cases improve the recovery of total RNA. For 30µl of lysate, add 20 ng of carrier RNA. Carrier RNA is not required when processing more than 500 cells or more than about 2 μg tissue. However, please bear in mind that for these small quantities, we would recommend the RNeasy Plus Micro Kit instead.