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Angular diameters have been estimated for 18 O and 142 B stars using absolute intermediate-band photometry in the near infrared and they have been combined with integrated fluxes to yield effective temperatures. The effective temperatures of the O stars lie in the range 30000 K to about 47000 K. For a given subtype, the luminosity class I stars have lower effective temperatures than the main-sequence stars by about 1000 K. The absorption-line spectral types of the supergiants of types O and B reflect electron temperatures which are higher than can be maintained by the integrated flux which flows through the stellar atmosphere. Distances have been estimated for all the stars and linear diameters found. The average radius for an 08 to 09.5 supergiant is about 23.3 R⊙; the radii for luminosity class III and Class V O stars lie in the range 6.8 to 10.7⊙ R.

We have made an extensive study of the far-UV extinction in SMC stars using IUE spectra mostly obtained by us. The studied stars are Sk 7, 13, 18, 32, 76, 82, 85, 103, 119, 124, 142, 143, 159, 191 and AV 398. A few other stars have also been observed but are unsuitable for extinction studies. We have obtained at ESO new photometry and spectral classifications for all the studied stars. The far-UV extinction curves derived from IUE spectra of matched star pairs are all similar, except for Sk 143 (Lequeux et al., 1982), Sk 124 and 191. The mean curve, which supersedes that of Rocca-Volmerange et al. (1981) is plotted Fig. 1 with the label SMC “normal”, as well as the curves for the three “anomalous” stars (full lines) For comparison, we also plot the LMC “normal” curve and that for the anomalous star Sk-69°108 (dotted-dashed curves), the “normal” galactic curve and the curves for two stars in Scorpius-Ophiuchus.