In the past two years we have investigated the systematics of the Arion hortensis aggregate, a complex assumed to be composed of three species, viz., A. hortensis Férussac, 1819 s.s., A. distinctus Mabille, 1868, and A. owenii Davies, 1979 (Davies, 1977, 1979; Backeljau, 1981; De Wilde, 1983; De Winter, 1984; Backeljau & Marquet, 1985). Elsewhere we have described the morphological variation in Belgian A. hortensis s.s. and A. distinctus (Backeljau, 1981; Backeljau & Marquet, 1985). It was concluded that the two Belgian forms can be distinguished quite easily on features of the genitalia. However, it was felt necessary to search for additional, clear-cut, evidence in order to demonstrate reproductive isolation between the two supposed species. Also, the systematic position of the third form, A. owenii, a rare species which is apparently endemic in Great Britain and Ireland (Davies, 1977, 1979), as well as the genital dimorphism in British A. distinctus (Davies, 1977, 1979; Backeljau & Marquet, 1985) needed to be evaluated. In order to achieve this, an electrophoretic survey of European A. hortensis s.l. has been initiated. Obviously in this kind of approach, it would be of primary interest if species specific protein patterns could be demonstrated. Such specific patterns, representing respectively A. hortensis s.s., A. distinctus and A. owenii, are presented in this paper for the first time.