Electrospinning (ES) silk fibroin (SF) offers attractive opportunities for producing matrixes (ES-SF mats) with great potential for tissue regeneration. Scanning electron microscopy (SEM) analyses showed that uniform ES-SF mats containing nanometric fibres were obtained by electrospinning a 7.5% w/v SF solution in formic acid, with an electric field of 2.4 kV cm(-1) and a spinneret collector distance of 10 cm. The structure of ES-SF mats before and after immersion in methanol (5, 10 and 15 min) was investigated by Fourier transform infrared (FT-IR) and differential scanning calorimetry (DSC) analyses. Crystallinity was enhanced by dipping time as shown by trends of FT-IR crystallinity index and DSC melting/decomposition temperature. Electrospun silk fibroin mats were seeded with L929 murine fibroblasts, incubated for 1, 3 and 7 days at 37 degrees C and, at each time point, SEM investigations and Alamar blue test were performed. The SEM images showed good cell adhesion after 1 day and cell confluence at the 7th day. Alamar blue test showed very low differences between cell viability on ES-SF mats and control.