Batch experiments with dry bracken fern have been done to determine cadmium and lead sequestering capacity of this biomaterial. Biomass characterisation was done by infrared spectroscopy and potentiometric analysis. The effect of pH of the metal containing solution, contact time and initial metal concentration has been studied, together with the acid-base properties of the biomaterial. Results obtained have been analysed using mathematical and modelling techniques. Effect of pH on metal sequestration has been correlated with observed acid-base properties of the natural substrate. Kinetic data analysis provided relevant information about metal sequestration rate, showing important differences between lead and Cadmium, Maximum uptake was found to be the same for both metals 0.410 mmol/g. This value was,also clearly correlated to the number of acidic groups determined for this material which was found to be 0.432 mmol of acidic groups per gram of fern. Results obtained indicate that acidic groups are the functional groups responsible of the sequestration of metal ions and that bracken fern is a promising material for metal preconcentration. (C) 2008 Elsevier Ltd. All rights reserved.