A method for the determination of a nucleic acid sequence, said method comprising the steps of: a) denaturing a double-stranded nucleic acid molecule corresponding to the said nucleic acid sequence, wherein at least one of the bases of one of the strands of the double-stranded nucleic acid is attached directly or indirectly to a support, and wherein at least one of the bases of the other strand of the double-stranded nucleic acid is attached to a movable support; b) hybridizing a single-stranded nucleic acid molecule, "the primer", with the said denatured double-stranded nucleic acid molecule; c) applying a tension to the hybridized primer/double-stranded nucleic acid molecule obtained in b); d) incubating the hybridized primer/double-stranded nucleic acid molecule obtained in step b) with a polymerase in conditions which will lead to at least one pause in replication; and e) determining the position of the said pause in replication with respect to one end of the double-stranded nucleic acid, said determination comprising the steps of: • measuring the distance (z) between the two ends of the double-stranded nucleic acid molecule which are attached to the support; • measuring the distance (z high) between the two ends of the double-stranded nucleic acid molecule which are attached to the support, when the said double-stranded nucleic acid molecule is denatured; and • comparing z and zhigh, and • determining the position of the pause, wherein the said double-stranded nucleic acid molecule is a hairpin. a) denaturing a double-stranded nucleic acid molecule corresponding to the said nucleic acid sequence, wherein at least one of the bases of one of the strands of the double-stranded nucleic acid is attached directly or indirectly to a support, and wherein at least one of the bases of the other strand of the double-stranded nucleic acid is attached to a movable support; b) hybridizing a single-stranded nucleic acid molecule, "the primer", with the said denatured double-stranded nucleic acid molecule; c) applying a tension to the hybridized primer/double-stranded nucleic acid molecule obtained in b); d) incubating the hybridized primer/double-stranded nucleic acid molecule obtained in step b) with a polymerase in conditions which will lead to at least one pause in replication; and e) determining the position of the said pause in replication with respect to one end of the double-stranded nucleic acid, said determination comprising the steps of: • measuring the distance (z) between the two ends of the double-stranded nucleic acid molecule which are attached to the support; • measuring the distance (z high) between the two ends of the double-stranded nucleic acid molecule which are attached to the support, when the said double-stranded nucleic acid molecule is denatured; and • comparing z and zhigh, and • determining the position of the pause, wherein the said double-stranded nucleic acid molecule is a hairpin. • measuring the distance (z) between the two ends of the double-stranded nucleic acid molecule which are attached to the support; • measuring the distance (z high) between the two ends of the double-stranded nucleic acid molecule which are attached to the support, when the said double-stranded nucleic acid molecule is denatured; and • comparing z and zhigh, and • determining the position of the pause, wherein the said double-stranded nucleic acid molecule is a hairpin.