GFP⁺ donor cells are detectable at NIMA-like levels 24 hours and 48 hours after injection into neonates. BALB/c neonates were injected intravenously with GFP⁺ adult spleen cells. Twenty-four or 48 hours later, spleens from individual mice were harvested for DNA, which was used in a GFP-specific real-time PCR assay. For quantitation, a standard curve consisting of DNA from a 0.001% to 1% GFP⁺ cell mixture was generated in parallel. The limit of sensitivity of this assay was 0.001% (dashed line). Individual animals from 3 independent experiments are shown.