Polycaprolactone (PCL) is a biocompatible aliphatic polyester with many possible applications in the medical field. PCL nanofibres, produced by electrospinning, could provide new characteristics that are of interest for these applications. However, a key prerequisite is the ability to obtain bead-free fibres with diameters in the nanoscale range. At present the most commonly used solvent for electrospinning PCL is chloroform, but this only leads to fibres in the microscale range. Therefore various solvent systems were examined in this study. The innovative solvent mixture formic acid/acetic acid was found to allow for nanofibres with a diameter 10 times smaller than the solvent chloroform. Moreover, steady state conditions could be obtained which thus allow electrospinning in a stable and reproducible way. Further it was noticed that the average fibre diameter decreased with decreasing polymer concentration while the diameter distribution decreased with increasing amount of formic acid. Also the humidity, an often overlooked yet important parameter, was noted to affect both diameter characteristics. Generally it can be concluded that the solvent system formic acid/acetic acid could fill the gap in electrospinning PCL since it is readily able to produce uniform fibres in the nanoscale range. © 2010 Elsevier Ltd. All rights reserved.