We have been able to hybridize nonradioactive probes from cell-type-specific genes to fixed whole-mounts prepared at the mound, slug, and culminant stages of Dictyostelium development. The cellular patterns of labeling with probes from the prespore gene, cotB, and the prestalk genes, ecmA and ecmB, confirmed the patterns seen in strains carrying reporter constructs in which the regulatory regions of these genes drive beta-galactosidase. This technique permits the direct observation of protein synthetic capacity from characterized genes without the need of generating transformed lines carrying specific reporter constructs. Moreover, the pattern is not complicated by a previous developmental history of gene expression.