A method for sorting a population of biological cells to detect a selected subpopulation thereof having a characteristic not shared by other cells of said population, said method comprising: (a) while cells of said population are in adherent form, (i) labeling cells of said subpopulation and cells not of said subpopulation with a photoactivatable fluorescent label that is capable of undergoing a transformation upon exposure to light energy, the transformation resulting in a detectable difference in the label as compared with a label that has not been exposed to said energy, wherein the detectable difference is retained upon converting labeled cells from adherent form to nonadherent form, (ii) identifying individual cells of said population belonging to said subpopulation or not belonging to said subpopulation, and (iii) specifically exposing the individual cells so identified to label-transforming energy to transform labels on cells so exposed; (b) subsequently converting cells in adherent form of said population to nonadherent form; and (c) while cells of said population are in nonadherent form, sorting said population to distinguish between cells of said subpopulation and cells other than said subpopulation by differentiating between cells with labels so transformed and cells with labels that have not been so transformed. (a) while cells of said population are in adherent form, (i) labeling cells of said subpopulation and cells not of said subpopulation with a photoactivatable fluorescent label that is capable of undergoing a transformation upon exposure to light energy, the transformation resulting in a detectable difference in the label as compared with a label that has not been exposed to said energy, wherein the detectable difference is retained upon converting labeled cells from adherent form to nonadherent form, (ii) identifying individual cells of said population belonging to said subpopulation or not belonging to said subpopulation, and (iii) specifically exposing the individual cells so identified to label-transforming energy to transform labels on cells so exposed; (i) labeling cells of said subpopulation and cells not of said subpopulation with a photoactivatable fluorescent label that is capable of undergoing a transformation upon exposure to light energy, the transformation resulting in a detectable difference in the label as compared with a label that has not been exposed to said energy, wherein the detectable difference is retained upon converting labeled cells from adherent form to nonadherent form, (ii) identifying individual cells of said population belonging to said subpopulation or not belonging to said subpopulation, and (iii) specifically exposing the individual cells so identified to label-transforming energy to transform labels on cells so exposed; (b) subsequently converting cells in adherent form of said population to nonadherent form; and (c) while cells of said population are in nonadherent form, sorting said population to distinguish between cells of said subpopulation and cells other than said subpopulation by differentiating between cells with labels so transformed and cells with labels that have not been so transformed.