A method for amplifying a nucleotide sequence contained in a target nucleic acid, comprising combining a target nucleic acid having a target nucleotide sequence with: (i) a polymerase, (ii) a first template that comprises a nucleic acid sequence comprising a first template recognition region at the 3' end that is complementary or substantially complementary to the 3' end of the complement of the first strand of the target nucleotide sequence, and a nicking enzyme binding site and nicking site upstream of the recognition region; (iii) a second template that comprises a nucleic acid sequence comprising a second template recognition region at the 3' end that is complementary or substantially complementary to the 3' end of the first strand of the target nucleotide sequence, and a nicking enzyme binding site and nicking site upstream of the recognition region; and (iv) one or more nicking enzymes capable of nicking at the nicking site of said first and second templates, wherein either one nicking enzyme is capable of nicking both of said templates, or each template is capable of being nicked by at least one of the nicking enzymes, wherein said one or more nicking enzymes do not nick within said target nucleotide sequence; wherein: the nucleotide sequence is amplified from a sample and the sample is added to the reaction mix or pre-diluted and then added to the reaction mix without prior purification of the target nucleic acid; wherein said sample contains spores, viruses or cells, or the sample is isolated from an animal and optionally comprises blood, bone marrow, mucus, lymph, hard tissues (e.g. liver, spleen, kidney, lung, or ovary), biopsies, sputum, saliva, tears, feces, or urine, or the sample may be a sample of waste water, drinking water, milk or other food, air, plant, soil, or other materials suspected of containing biological organisms, and interaction of the templates with the target nucleic acid and the nicking and template extension reactions are conducted under isothermal conditions and without a denaturation step. (i) a polymerase, (ii) a first template that comprises a nucleic acid sequence comprising a first template recognition region at the 3' end that is complementary or substantially complementary to the 3' end of the complement of the first strand of the target nucleotide sequence, and a nicking enzyme binding site and nicking site upstream of the recognition region; (iii) a second template that comprises a nucleic acid sequence comprising a second template recognition region at the 3' end that is complementary or substantially complementary to the 3' end of the first strand of the target nucleotide sequence, and a nicking enzyme binding site and nicking site upstream of the recognition region; and (iv) one or more nicking enzymes capable of nicking at the nicking site of said first and second templates, wherein either one nicking enzyme is capable of nicking both of said templates, or each template is capable of being nicked by at least one of the nicking enzymes, wherein said one or more nicking enzymes do not nick within said target nucleotide sequence; the nucleotide sequence is amplified from a sample and the sample is added to the reaction mix or pre-diluted and then added to the reaction mix without prior purification of the target nucleic acid; wherein said sample contains spores, viruses or cells, or the sample is isolated from an animal and optionally comprises blood, bone marrow, mucus, lymph, hard tissues (e.g. liver, spleen, kidney, lung, or ovary), biopsies, sputum, saliva, tears, feces, or urine, or the sample may be a sample of waste water, drinking water, milk or other food, air, plant, soil, or other materials suspected of containing biological organisms, and interaction of the templates with the target nucleic acid and the nicking and template extension reactions are conducted under isothermal conditions and without a denaturation step.