The nucleotide sequence of the internal transcribed spacer (ITS) 1 and 2 regions was determined for 22 Suillus isolates representing seven species. Analysis of the sequence data along with 12 related sequences from databases divided the 34 isolates into seven groups, and six of these were supported by 100% bootstrap values. Isolates belonging to Suillus granulatus (0-11 divergence) were divided into three groups (SG1, SG2 and SG3); SG1 and SG2 had 100% bootstrap values. SG2 was clustered with two Suillus collinitus isolates and a Suillus variegatus isolate; SG3 was linked to a previously characterised Suillus subluteus isolate. These results clearly indicate heterogeneity among the isolates described under these species. Intra- (0.4-11) and inter- (2.4-13.6) specific divergence varied considerably. Suillus laricinus showed a high level (0.5-4.4) of intra-specific divergence. Suillus bovinus showed maximum divergence (11.4-13.3) to all other species examined. The potential of the ITS region for understanding the intra- and inter-specific relationships among Suillus species and refining their taxonomy is discussed.