Abundance determination from H II regions in NGC 2403.

We present photoelectric spectrophotometry in the 3400-74O0Å range for five HII regions in the spiral galaxy NGC2403. The ionic abundances of He+, N+, O+, O++, Ne++, S+ and Ar++ relative to H+, as well as the total N and O abundances are derived. Gradients in electron temperature, He/H, N/H and O/H were found. By comparing N/O and O/H values with chemical evolution models by Serrano and Peimbert (1983) and Tosi and Diaz (1985) a lower H2 abundance is supported such as the one proposed by Bhat . (1986).