Results of a spectrophotometric survey in the magellanic barred galaxy
NGC 2366 and in the small weakly barred spiral galaxy NGC 4395, emplo
ying imaging spectrophotometry with narrow-band interference filters i
n the lines of H alpha, H beta, [O III] lambda 5007 and [N II] lambda
6584, are presented. The use of [O III]/H beta as an abundance indicat
or is assessed; it is shown that for the probable range of the physica
l properties of the H II regions in NGC 2366 and NGC 4395, [O III]/H b
eta may not give reliable estimates of O/H abundances in the interstel
lar gas in these two low-mass galaxies. Instead we use [N II]/[O III],
which is more dependable at relatively low abundances. The derived me
an levels of O/H (+/-1 sigma dispersion) in NGC 2366 and NGC 4395 are
12 +/- log O/H = 8.19 +/- 0.14 and 8.33 +/- 0.25, respectively; the gl
obal gradients of both galaxies are flat. Mechanisms which could expla
in the absence of abundance gradients in low-mass and irregular galaxi
es are explored.