Observation	Suggested trouble shooting check-list
No signals or weak signals	Preservation of target nucleic acids
	Ribonuclease contamination
	Preservation of tissue
	Conditions of protease digestion
	Choice of probe
	Labelling of probe
	Amount of probe used in hybridization
	Hybridization conditions and buffer
	Heat denaturation of DNA probe or target
	Reagents used in the detection steps
	Use appropriate positive control to diagnose the problem
High background	Improve or use extra pretreatment steps
	Amount of probe used in hybridization steps
	Choice of hybridization conditions and buffer used
	Choice of washing conditions and buffer used
	Use appropriate controls to diagnose the problem
Detached section	Tissue preparation and fixation
	TESPA coating of slides
	Optimize conditions of protease digestion and post-fixation