Expression of endoribonuclease VI activity during early larval development of the crustacean Artemia has been studied in vivo in the presence of different inhibitors of transcription and translation. All the transcription inhibitors tested (α-amanitin, cordycepin and actinomycin D) did not affect the expression of the activity. However, protein synthesis inhibitors (cycloheximide and anisomycin) prevented the appearance of the activity. These data strongly indicate that the control of the expression of endoribonuclease VI is carried out post-transcriptionally.