RESUMEN
The present work studies the ability of cytoarabine (Ara C) to modify temporal regulation of hemoglobin synthesis in chicken embryos. Thus different concentrations of Ara C were injected into fertilized chicken eggs after 94 hours of incubation. Blood samples were taken from both treated and control embryos on the 7th and 8th day of incubation. 1) Ara C 4.1 x 10(-3) M: embryo mortality is total and takes place upon injection. 2) Ara C 4.1 x 10(-5) M: no significant difference was seen between hemoglobin patterns in the treated and control embryos. 3) Ara C 4.1 x 10(-4) M: a delay of at least 24 hours in hemoglobin switch-over is seen in the treated embryos. In fact, at the 7th day adult hemoglobin fractions A and D have not yet appeared while, on the 8th day, embryonic fraction P is still present.