1987; McHardy et al. 1995).

X-ray observations were made with the [*Rossi X-Ray Timing Explorer (RXTE)*]{}, and optical spectra were obtained with ground-based telescopes, as described below. The purpose of this program has been twofold:

1.  To determine the nature of the relationship between the X-ray and UV–optical continuum variations. This is a particularly interesting question in the case of NGC 4051 since the X-ray flux dropped to an extremely low level in 1998 May (Uttley et al. 1999), towards the end of this campaign.

2.  To determine the BLR size and virial mass via reverberation techniques.

In this contribution, we present the results of this program, and discuss their implications for the nature of the NLS1 phenomenon.

Observations and Data Analysis
==============================

X-Ray Observations
------------------

The X-ray observations were made with the large area (0.7 m$^{2}$) Proportional Counter Array (PCA) on [*RXTE*]{} (Bradt, Rothschild & Swank 1993). The observations shown here, which are part of a continuing monitoring program, cover the period from 1996 March to 1998 June. The observations were scheduled initially to cover the largest range of variability time scales with the smallest number of observations in order to determine the X-ray power spectrum efficiently. The program 