Developmentally regulated gene expression has been analyzed in the wild-type D. discoideum strain NC-4 and a series of temporally deranged mutants. The mutants include representatives from each class of rapid development mutation, Fr17(rdeA-) and HT506(rdeC-), and strain HIfm-1, which appears to be defective in the timing of events early in development. We have monitored four prespore-specific genes, three of which show coordinate expression in the wild type. The coordination is maintained in each of the mutant strains though the specific expression pattern varied from strain to strain. Likewise, a series of prestalk-specific genes have been analyzed. They also show coordinated expression in the wild type and in all of the mutants. The timing of expression, however, is different between the prestalk-specific and the prespore-specific with the overall pattern of expression being unique for each strain examined. These results confirm our previous suggestion that the major classes of prestalk- and prespore-specific genes are coordinately regulated and show that a great deal of tolerance is allowed in the timing of specific gene expression as it relates to terminal differentiation. In addition we have analyzed the expression of actin, discoidin I, and I42. These genes, or gene families, are preferentially expressed in either vegetatively growing cells or in cells during the early stages of development. As with the cell-type-specific genes, the pattern of expression of the three early gene classes is unique for each strain examined.