1 Introduction

Popescu et al. (1996, 1998) conducted a survey for emission-line galaxies (ELGs) based on the Hamburg Quasar Survey (HQS, Hagen et al. 1995) - IIIa-J digitised objective prism plates. The main goal of the project was to search for dwarf ELGs in voids and to analyse the large-scale structure of the distribution of this kind of galaxies (Popescu et al. 1997). The follow-up spectroscopy at the 2.2m telescope at the German-Spanish Observatory at Calar Alto (Almeria, Spain) provided us with a complete sample of 250 ELGs, of which many are Blue Compact Dwarfs (BCDs) or HII galaxies. These two terms are usually used to define the same kind of objects. While the name BCD was mainly used for objects classified on morphological criteria (Binggeli et al. 1985 - for the Virgo Cluster Catalogue), the term of HII galaxy was introduced for objects discovered on spectroscopic surveys for emission-line galaxies. These objects have focused attention after the discovery by Sargent & Searle (1970) that some of them were low metallicity systems hosting a very active stellar formation. Gallagher & Hunter (1989) showed that the BCDs present also the lowest mass surface density and rotation velocities ever measured for objects supporting star formation activity. Thus it was suggested (Vilchez 1995) that these galaxies can be easily affected by environmental factors. Since in our study of the spatial distribution of ELGs (Popescu et al. 1997) we identified the isolation of each sample galaxy, we can address the question of environmental influences on the star-forming properties of HII galaxies, using an unbiased sample. In this paper we give the catalogue of the spectroscopic parameters of a subsample of 90 ELGs and we describe the data sample. The influence of the environment on the mechanism that controls star formation is discussed in a separate paper (Popescu et al. 1999).