Compounds of formula (I) and salts thereof: wherein R1 is n-C4-6alkyl or C1-2alkoxyC1-2alkyl-; R2 is hydrogen or methyl; each R3 is hydroxy, halo or n-C1-3alkyl; m is an integer having a value of 2 to 4; n is an integer having a value of 0 to 3; and p is an integer having a value of 0 to 2, are inducers of human interferon. Compounds which induce human interferon may be useful in the treatment of various disorders, for example the treatment of allergic diseases and other inflammatory conditions, for example allergic rhinitis and asthma, infectious diseases and cancer, and may also be useful as vaccine adjuvants.