Primary objective: To study the pharmacokinetic interaction between zidovudine (AZT) and valproic acid in asymptomatic HIV-infected patients, characterizing AZT's oral bioavailability, plasma elimination half-time, plasma levels, and urinary excretion of AZT, 5'-O-glucuronide (GAZT), and 3'-amino-3'-deoxythymidine (AMT). Secondary objective: To establish the safety of short-term administration of AZT and valproic acid in combination with regard to hematologic parameters and liver function in asymptomatic HIV-infected patients.