I've been told by a knowledgeable contractor that it can make sense to first have your home tested by an independent inspector if you have reason to believe you have a mold problem. While the remediation companies may also do testing, they would benefit more the more serious your problem is. An independent inspector wouldn't be biased. If you have a home tested and there is a mold problem, then you would need to contact a Certified Mold Remediator.
Mold Inspections
JMR Environmental
Mold Fixer
Mold Inspections and Lab Tests
Precision Mold Testing
Mold Remediation
Alliance
Clean Earth Carpet
In Home Clean
J M Keystone
Mold Happens