I t can be tricky to search the Internet for answers to health questions -- because mixed in with a bounty of valid information are countless unsubstantiated claims and even some downright dangerous advice.

Best: Put your faith in the following reliable Web sites. For information on...

Diagnosis and treatment: www.MayoClinic.com.

Features: Reports on symptoms, causes, complications, tests, treatments and coping strategies for thousands of illnesses... Multimedia presentations... Links to disease-specific organizations.

Click-worthy: "Health Manager," a free personalized program for monitoring and managing your own and your family’s health.

Drugs and supplements: www.Drugs.com.

Features: Consumer-friendly information on uses, dosages, side effects and contraindications for prescription and nonprescription drugs, herbs and dietary supplements... Interactions checker -- to see if the effect of a particular drug is altered when it is taken with another drug, supplement or food... New drug approvals and alerts from the FDA.

Click-worthy: "Pill identifier" (including photos) that searches by color, shape and/or imprint.

Integrative medicine: www.NaturalStandard.com.

Features: Free e-newsletter... Blogs and newsfeed... In-depth databases on thousands of herbs and supplements (requires a paid subscription).

Click-worthy: Webinars on alternative medicine.

Lifestyle and spiritual well-being: www.LifeScript.com.

Features: Blogs from doctors, psychologists, nutritionists, fitness experts and alternative health-care providers... Calculators for body mass index, calorie burn and more... Six free e-newsletters.

Click-worthy: Quizzes that test your knowledge (for instance, on acupuncture or hygiene) or assess your risk (such as for cancer or depression).

Natural health and healing: www.NaturalNews.com.

Features: Breaking news reports... Cartoons and satire... "Citizen journalism" program that invites articles from independent writers.

Click-worthy: Podcasts from author Mike Adams (aka "Health Ranger") interviewing preeminent experts on alternative medicine.

Scientific studies: www.PubMed.gov.

Features: More than 19 million citations for biomedical articles dating back to 1948... Interactive tutorials on newsworthy topics, such as flu outbreaks... MedlinePlus, consumer-friendly versions of thousands of health-related articles.

Click-worthy: ClinicalTrials.gov, a locator for studies recruiting participants.

Symptom identification: www.HealthCentral.com.

Features: Health and drug library... Expert Q & A... Community of members who share experiences and advice.

Click-worthy: "Check a Symptom," a step-by-step function that leads you through a diagnostic process and treatment options.