Isoschizomers are pairs of restriction enzymes specific to the same recognition sequence.
In some cases, only one out of a pair of isoschizomers can recognize both the methylated as well as unmethylated forms of restriction sites.
This property of some isoschizomers allows identification of methylation state of the restriction site while isolating it from a bacterial strain.
For example, the restriction enzymes HpaII and MspI are isoschizomers, as they both recognize the sequence 5'-CCGG-3' when it is unmethylated.
An enzyme that recognizes a slightly different sequence, but produces the same ends is an isocaudomer.