Recent speculation as to whether material obtained by needle biopsy can be used to study physiological properties of single muscle fibres, led us to investigate whether fibre segments obtained by this procedure, exhibit the same contractile characteristics as those fibre segments obtained from ablated whole muscles. Needle biopsies were taken of the upper hindlimb from adult, Sprague-Dawley rats, killed by diethyl ether overdose. Single muscle fibre segments were isolated by microdissection, mechanically skinned (sarcolemma removed) and attached to a sensitive force recording transducer to measure Ca(2+)- and Sr(2+)-activated responses. No significant differences were found in Ca(2+)- and Sr(2+)-activated contractile characteristics (including maximum force generation) between fibres sampled by needle biopsy and those dissected from ablated intact muscles. Needle biopsied muscle fibre segments maintained their characteristic properties for up to 6-8 h (after sampling) if kept at room temperature in paraffin oil, and for up to 36 h if refrigerated (2-5 degrees C) in paraffin oil immediately after the biopsy procedure. It is concluded that muscle fibres sampled by needle biopsy have similar properties to fibres isolated from ablated muscles.