From January 1989 to December 1990, stool samples from 288 children with enteritis were examined for the presence of unusual campylobacters which represented about 20% of all campylobacteria isolated when the filtration technique was used. The isolation percentage was the following: C. jejuni ss. jejuni 6.9%; C. coli 2%; C. jejuni ss. doylei, C. upsaliensis and C. concisus each 0.7%. The atypical Campylobacter isolates were examined for their virulence characteristics. Toxin profiles based on cytotonic, cytotoxic and cytolethal distending factors were determined after analysis responses in Vero, CHO and HeLa cells. Adhesivity and invasivity tests were performed on Intestine 407 cells. No strain was cytotoxic. C. jejuni ss. doylei and C. concisus induced an elongation of CHO cells (a cytotonic-like effect). C. upsaliensis strains provoked a cytolethal distending effect. No strain adhered to cells in vitro. Our results suggest that the filtration technique is excellent for the isolation of atypical campylobacters and indicate that the unusual Campylobacter isolates could be potentially virulent.