The invention provides a group of oligonucleotide probes in which the individual probes are capable of hybridizing to specific gene sequence variations so as to permit detection of said variations when said probes are labelled and so-hybridized, whereby allelic variations and gene polymorphism in samples may be detected using said group of probes. Such probe groups are useful for detecting nucleotide variations, mutations and polymorphisms by hybridization to amplified nucleic acid sequence containing such variations, mutations or polymorphisms.