5-Oxo-1, 2, 3, 5-tetrahydro-5H-imidazo [1, 2-b] isoquinoline (IIa) and related compounds were synthesized from homophthalic acid and an aliphatic 1, 2- or 1, 3-diamine. In addition, homophthalic acids or o-carboxyphenylmalonic acid diesters were allowed to react with an aliphatic 1, 2- or 1, 3-aminoalcohol or aminothiol with heating in the presence of p-toluenesulfonic acid, yielding a series of oxazolo- or oxazino-isoquinolones (VI) or thiazolo- or thiazino-isoquinolones (IV). Oxidation of IV gave the corresponding sulfoxides (VII) and sulfones (VIII). Treatment of o-cyanomethylbenzenesulfonyl chloride with an N-alkyl 1, 2- or 1, 3-diamine gave N-alkyl-imidazo- or pyrimido-benzothiazine-5, 5-dioxide (XI). The compounds thus prepared were evaluated for their anti-inflammatory effect in rats, using the carrageenin paw edema method, and some of the condensed heterocyclic isoquinolone derivatives were found to exhibit strong anti-inflammatory activity. These compounds were also examined for analgesic activity in terms of the inhibition of acetic acid induced writhing. Compound VIIIk showed stronger anti-inflammatory activity than phenylbutazone, as well as analgesic activity comparable to that of aminopyrine, and had very low toxicity.