Trypsinize cells and stop with medium. Mix and count the cells. Use 4 x 104 cells per well in 6-well dishes. Dilute cells to 4 x 104 cells per ml of medium in 2x 3T3 medium. Final volume will be 2 ml per well.
Heat agar in microwave until melted.
Place in 50 C waterbath to cool. It is ready when you can hold the bottle in your hand without pain. Aliquot into wells and let harden. Cap and mix quickly. Pour into wells.