We have examined the spatial and temporal patterns of expression of the Krüppel (Kr) protein, a gap gene product, during Drosophila embryogenesis. Antibodies directed against the Kr protein revealed patterns of nuclear staining that represent subpatterns of Kr transcript accumulation in particular tissues. This indicates that the distribution of Kr protein is not a direct response to Kr mRNA accumulation, and that Kr protein expression requires a second level of control in addition to spatially regulated transcription. Our data provide evidence for posttranscriptional control that may involve an intron present in the 5' region of one of the two Kr transcripts. The intron-containing transcript is the only potential source of new Kr protein synthesis after gastrulation. The finding of late and transient patterns of Kr activity in several tissues, such as the developing nervous system, amnion serosa, and muscle precursor cells suggests that Kr activity may be required in several developmental processes after segmentation has been completed.