query on mysql binary fields

Hi, I've some problem in order to use a binary fields by a simple query .... I use a query like "SELECT field FROM table WHERE field='value'" where "field" is a char(8) BINARY and "value" is an alphanumeric string (like this: MMl045aA) ... the problem is that my query always returns 0 (not found) ... More strange is if I use a value like 12345678 (just number) instead of an alphanumeric string, my query found the occurence .... I've repeatevly checked the php syntax code and all seems work fine except for the case sensitive query ... Anyone could help me please? Many thanks in advance max