Correspondence pertaining to material published in the Journal will be published, if found suitable, as space permits. Submit double-spaced copy clearly marked "For publication" and signed by all authors; references should conform to Journal format; maximum length: 500 words. Copyright assignment signed by all authors is required. The Editor reserves the right to edit such letters, which should be received within six weeks of publication of the Journal article in question. Sir.—We read with interest the report of Kelly et al, "Monitoring Children on Sustained-Release Therapy by Salivary Theophylline Levels" (Journal 1981;135:137-139). Despite several encouraging reports on the usefulness and reliability of salivary theophylline concentrations,1,2 subsequent studies have failed to support these findings.3 In a recent investigation of the bio-availability and release pattern of a sustained-release theophylline (TheoDur), we had the opportunity to examine serum-saliva theophylline ratios in six healthy young adults.
Subjects were administered theophylline, 600