| Abstract
| - Results of a ground-based optical monitoring campaign on NGC 5548 in June 1998 are presented. The broad-band fluxes ( U, B, V), and the spectrophotometric optical continuum flux $F_\lambda$ (5100 Å) monotonically decreased in flux while the broad-band R and I fluxes and the integrated emission-line fluxes of H α and H β remained constant to within 5% . On June 22, a short continuum flare was detected in the broad band fluxes. It had an amplitude of about ~18% and it lasted only ≈90 min. The broad band fluxes and the optical continuum $F_\lambda$ (5100 Å) appear to vary simultaneously with the EUV variations. No reliable delay was detected for the broad optical emission lines in response to the EUVE variations. Narrow H β emission features predicted as a signature of an accretion disk were not detected during this campaign. However, there is marginal evidence for a faint feature at $\lambda \simeq 4962$ Åwith $FWHM\simeq 6$ Åredshifted by $\Delta v\simeq 1100$ km s -1 with respect to H $\beta _{\rm narrow}$.
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