(A) NIH 3T3 cells were incubated with PTD.AdeGFP, Ad.eGFP:CaPi (calcium phosphate precipitated AdeGFP) and AdeGFP at 4°C for 1 h. The cells were washed by 2% (v/v) DMEM medium or treated with trypsin. The cells were incubated for a further 48 h at 37°C and the cells were analysed by FACS. Results are means±S.D. (n=4) and statistical significance was determined by the Student's t test. (B) Cells treated as in (A) were imaged at ×20 magnification using an Olympus IX70 microscope.