linear wound designated here as a wound healing zone whz wound of this diameter were routinely and reproducibly made by this technique and allow study of the effect of any agent that might have an effect on wound healing by measuring the delay in time it takes to fill in the wound gap of the whz fig6 is a photograph of 9 culture dishes fixed with 50 ethanol and stained with 0 2 crystal violet 24 hours after forming the whz and incubated in the serum free medium of this invention containing varying doses of retinyl acetate the experiment was performed in duplicate dishes there is only one dish labeled 3e 5 as its duplicate was contaminated with mold and was eliminated control dishes were refed serum free medium supplemented with insulin but no retinyl acetate all of the other dishes were r3efed serum free medium with insulin and increasing amount of retinyl acetate the mi9d line whz was filled by epidermal keratinocyte migration and cell growth in all of the dishes except for cultures that had retinyl acetate at concentrations greater than 3 u00d7 10 sup u2212 6 m fig7 show photomicrographs comparing wound closure in the whz for cultures of hacat keratinocytes fixed and stained with crystal violet stain and photographed with bright field illumination fig7 a shows complete failure to fill.