Analyses of the Null Subject Parameter (NSP) suggest that several factors may influence the resetting process for second language acquisition, such as specific "trigger" data, awareness of agreement as a part of awareness of agreement (INFL), and stylistic rules such as subject postposing and anaphoric reference. Four tests were administered to two groups of second language students, Spanish speakers acquiring English as a Second Language (ESL) and English speakers acquiring Spanish as a Second Language (SSL), to elicit production and receptive data in constructions involving NSP. It was hypothesized that ESL subjects would show slower resetting of the parameter than SSL subjects. Three subject types (pronouns, "there/hay", and "it/es" existentials) were used in imitation, written production, oral production, and grammaticality judgment tasks. SSL subjects did reset the parameter more quickly. On all tasks, SSL subjects omitted subjects in "hay/es" constructions and showed variable use with pronominal subjects. SSL subjects showed an awareness of discourse factors in subject usage, but little use of stylistic inversion. Findings imply that for SSL, existentials may be "trigger" constructions. ESL subjects appeared to reset the parameter for pronominals but not existentials and still showed considerable subject deletion in "there/it" constructions at the end of the study period. For neither group was agreement a factor in determining subject use. (Author/MSE)