I have been trying to grow MRC-5 cells for quite some time. After changing 3 source it still doesn't grow fast enough to do experiment. The cell morphology looks fine visually. I use MEM with 10% FBS, 1% Penicillin Streptomycin, and 1% Non-Essential Amino acids. Change the media each 2-3 days. First I thought its a problem with initial cell inoculation density, so I subsequently tried to put them in smaller surface. With each subculture around 50% cells doesn't survive so the smaller surface area have no effect. Please suggest if you have any solution other than what i mentioned above. Thank you.